Charged Particle Beam Apparatus and Sample Image Acquiring Method

ABSTRACT

Disclosed is a charged particle beam apparatus wherein a partitioning film capable of transmitting a charged particle beam is provided between a charged particle optical system and a sample, said charged particle beam apparatus eliminating a contact between the sample and the partitioning film even in the cases where the sample has recesses and protrusions. On the basis of detection signals or an image generated on the basis of the detection signals, a distance between a sample and a partitioning film is monitored, said detection signals being outputted from a detector that detects secondary charged particles discharged from the sample due to irradiation of a primary charged particle beam.

TECHNICAL FIELD

The present invention relates to a charged-particle beam apparatus thatis able to observe a sample under atmospheric pressure or apredetermined pressure of non-vacuum.

BACKGROUND ART

In order to observe a minute area of an object, a scanning electronmicroscope (SEM), a transmission electron microscope (TEM), or the likeis used. Generally, in these apparatuses, a housing is evacuated fordisposing a sample, an atmosphere of the sample is in a vacuum state,and then the sample is imaged. However, a biochemical sample, a liquidsample, or the like is damaged by vacuum, or the state thereof ischanged. On the other hand, since needs to want to observe are large,such a sample with the electron microscope, the SEM apparatus which isable to observe the sample to be observed under atmospheric pressure,has been strongly desired.

Therefore, in recent years, a SEM apparatus, in which a sample is ableto be disposed under atmospheric pressure by partitioning to be a vacuumstate and an atmospheric state by providing an electron beam permeablemembrane between an electron optical system and the sample, has beendisclosed. In the apparatus, in a state where the membrane and thesample do not come into contact with each other by using a sample stagedisposed just below the membrane, it is possible to change a sampleposition and to perform SEM observation under atmospheric pressure.

CITATION LIST Patent Literature

PTL 1: JP-A-2012-221766

SUMMARY OF INVENTION Technical Problem

In an apparatus that irradiates the sample disposed under atmosphericpressure with a charged-particle beam in a state where the membrane andthe sample do not come into contact with each other, image quality isimproved if the membrane and the sample are close to each other.However, if the sample and the membrane are too close to each other, thesample and the membrane come into contact with each other and therebythere is a concern that the membrane is damaged. A method, in which thesample and the membrane do not come into contact with each other bydisposing a contact prevention member, of which a thickness is known,between a member maintaining the membrane and the sample, is describedin PTL 1. However, since the contact prevention member is disposedoutside more than the membrane, if the sample is not flat and is uneven,there is a problem that the contact prevention member cannot preventdamage of the membrane.

The invention is made in view of such a problem and an object of theinvention is to provide a charged-particle beam apparatus that is ableto observe a sample at atmospheric pressure or a gas atmosphere byadjusting a distance between a membrane and the sample without damagingthe membrane, and a sample image acquiring method that uses theapparatus.

Solution to Problem

In order to solve the problem described above, the invention uses acharged-particle beam apparatus including a charged-particle opticalcolumn that irradiates a sample with a primary charged-particle beam; ahousing that forms a part of the charged-particle beam apparatus andthat has an inside thereof which is evacuated by a vacuum pump; amembrane which is able to maintain an airtight state of a space which isevacuated and through which the primary charged-particle beam transmitsor passes; and a detector that detects secondary charged-particles thatare emitted from the sample by application of the primarycharged-particle beam, in which a distance between the sample and themembrane is monitored based on a detection signal that is output fromthe detector or an image that is generated from the detection signal.

Advantageous Effects of Invention

According to the invention, since the distance between the sampledisposed just below the membrane and the membrane can be monitored, itis possible to adjust the distance between the membrane and the samplewithout contacting the sample disposed under atmospheric pressure, or anatmosphere of a substantially equal pressure, with the membrane.

Problems, configurations, and effects other than the above descriptionwill become apparent from the following description of embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an entire configuration view of a charged-particle microscopeof Example 1.

FIG. 2 is an explanatory view of a principle in Example 1.

FIG. 3 is an explanatory view of the principle in Example 1.

FIG. 4 is an explanatory view of the principle in Example 1.

FIG. 5 is an explanatory view of signal detection in Example 1.

FIG. 6 is an explanatory view of the signal detection in Example 1.

FIG. 7 is an explanatory view of the signal detection in Example 1.

FIG. 8 is an explanatory view of an execution flow in Example 1.

FIG. 9 is an explanatory view of the signal detection in Example 1.

FIG. 10 is an explanatory view of the signal detection in Example 1.

FIG. 11 is an explanatory view of the execution flow in Example 1.

FIG. 12 is a configuration view of a charged-particle microscope ofExample 2.

FIG. 13 is an operation screen of the charged-particle microscope ofExample 2.

FIG. 14 is a configuration view of a charged-particle microscope ofExample 3.

FIG. 15 is a configuration view of a charged-particle microscope ofExample 4.

FIG. 16 is a configuration view of a charged-particle microscope ofExample 5.

FIG. 17 is a configuration view of a charged-particle microscope ofExample 6.

FIG. 18 is an explanatory view of a difference in detection signals in agas pressure in Example 6.

FIG. 19 is a configuration view of the charged-particle microscope ofExample 6.

FIG. 20 is a configuration view of the charged-particle microscope ofExample 6.

DESCRIPTION OF EMBODIMENTS

Hereinafter, each embodiment will be described with reference todrawings.

Hereinafter, as a charged-particle beam apparatus, a charged-particlebeam microscope will be described. However, this is merely an example ofthe invention and the invention is not limited to the followingembodiments. The invention may also be applied to a scanning electronmicroscope, a scanning ion microscope, a scanning transmission electronmicroscope, a composite apparatus of these microscopes and a sampleprocessing device, or an analysis and inspection apparatus applyingthese devices.

In addition, in this specification, “atmospheric pressure” is an airatmosphere or a predetermined gas atmosphere, and means a pressureenvironment of atmospheric pressure or a slightly negative pressure.Specifically, it is approximately from 10⁵ Pa (atmospheric pressure) to10³ Pa.

Example 1 Apparatus Configuration

In the embodiment, a basic embodiment will be described. FIG. 1illustrates an entire configuration view of a charged-particlemicroscope of the example.

The charged-particle microscope illustrated in FIG. 1 is mainlyconfigured of a charged-particle optical column 2, a housing (vacuumchamber) 7 connected to the charged-particle optical column 2, a samplestage 5 disposed under atmosphere pressure, and a control systemcontrolling these members. When using the charged-particle microscope,insides of the charged-particle optical column 2 and the housing 7 areevacuated by a vacuum pump 4. Actuation and stop operation of the vacuumpump 4 are also controlled by the control system. Only one vacuum pump 4is illustrated in FIG. 1, but two or more vacuum pumps may be provided.The charged-particle optical column 2 and the housing 7 are supported bya pillar or a base (not illustrated).

The charged-particle optical column 2 is configured of elements such asa charged-particle source 8 that generates the charged-particle beam andoptical lenses 1 that guide the generated charged-particle beam to thelower portion of the column by focusing the charged-particle beam andscan a sample 6 with a primary charged-particle beam. Thecharged-particle optical column 2 is disposed so as to protrude to theinside of the housing 7 and is fixed to the housing 7 via a vacuumsealing member 123. A detector 3 that detects secondarycharged-particles (secondary electrons or reflected electrons) obtainedby application of the primary charged-particle beam is disposed in theend portion of the charged-particle optical column 2. The detector 3 maybe provided on an outside or an inside of the charged-particle opticalcolumn 2. In addition, other lenses, electrodes, and detectors may beincluded in the charged-particle optical column, a part of them may bedifferent from the others, and a configuration of a charged-particleoptical system included in the charged-particle optical column is notlimited to the example.

The charged-particle microscope of the example includes a computer 35that is used by a user of the apparatus, an upper control section 36that is connected to the computer 35 and performs communication with thecomputer 35, and a lower control section 37 that performs controls of aevacuation system, a charged-particle optical system, and the like inaccordance with commands transmitted from the upper control section 36as a control system. The computer 35 includes a monitor 33 on which anoperation screen (GUI) of the apparatus is displayed and an input unitsuch as a keyboard and mouse to the operation screen. The upper controlsection 36 is connected to the lower control section 37 and the computer35 by each of communication lines 43 and 44.

The lower control section 37 is a portion that transmits and receivescontrol signals for controlling the vacuum pump 4, the charged-particlesource 8, the optical lenses 1, and the like, and transmits outputsignals of the detector 3 to the upper control section 36 by convertingthe output signals into digital image signals. An image generated by theupper control section 36 is displayed on the monitor 33 of the computer35. In the view, the output signal from the detector 3 is connected tothe lower control section 37 via an amplifier 154 such as apreamplifier. If the amplifier is not necessary, the amplifier may notbe provided.

In the upper control section 36 and the lower control section 37, analogcircuits, digital circuits, and the like may be mixed. The upper controlsection 36 and the lower control section 37 may be integrated. Inaddition, a control section that controls an operation of each portionmay be included in the charged-particle microscope. The upper controlsection 36 or the lower control section 37 may be configured of hardwareby a dedicated circuit substrate or may be configured of software thatis executed by the computer 35. When being configured of the hardware,it is possible to realize the hardware by integrating a plurality of thecalculators executing processing on a wiring substrate, or within asemiconductor chip or a package. When being configured of the software,it is possible to realize the software by executing a program thatexecutes a desired calculation processing by mounting a high-speedgeneral-purpose CPU to the computer. Moreover, the configuration of thecontrol system illustrated in FIG. 1 is merely an example andmodification examples of a control unit, a valve, the vacuum pump,communication wiring, and the like belong to the category of design ofthe SEM and the charged-particle beam apparatus of the example, as longas functions intended in the example are satisfied.

A vacuum pipe 16, an end of which is connected to the vacuum pump 4, isconnected to the housing 7 and the inside thereof can be maintained in avacuum state. Simultaneously, a leakage valve 14 for opening the insideof the housing to the atmosphere is provided and the leakage valve 14can open the inside of the housing 7 to the atmosphere duringmaintenance and the like. The leakage valve 14 may be not provided ormay be two or more. In addition, an arrangement position of the leakagevalve 14 in the housing 7 is not limited to the portion illustrated inFIG. 1 and may be arranged in another position on the housing 7.

A membrane 10 is provided in a position just below the charged-particleoptical column 2 on a lower surface of the housing. The membrane 10 isable to cause the primary charged-particle beam emitted from a lower endof the charged-particle optical column 2 to transmit or pass and theprimary charged-particle beam finally reaches the sample 6 mounted on asample stage 52 through the membrane 10. A closed space (that is,insides of the charged-particle optical column 2 and the housing 7)configured of the membrane 10 is able to be evacuated. Since the sampleis disposed in a non-vacuum space, the membrane 10 is necessary formaintaining differential pressure between a vacuum space and thenon-vacuum space. In the example, since an airtight state of the spaceevacuated by the membrane 10 is maintained, it is possible to maintainthe charged-particle optical column 2 in the vacuum state and to observethe sample 6 by maintaining the sample 6 at atmospheric pressure. Inaddition, even in a state where the charged-particle beam is applied,since the space in which the sample is disposed is in the air atmosphereor communicates with a space of the air atmosphere, the sample 6 can befreely exchanged during observation.

The membrane 10 forms a film or is deposited on a base 9. The membrane10 is a carbon material, an organic material, a metal material, siliconnitride, silicon carbide, silicon oxide, and the like. The base 9 is,for example, a member such as silicon or a metal member. The membrane 10may be a plurality of arranged multi-windows. A thickness of themembrane through which the primary charged-particle beam can betransmitted or can pass is approximately several nm to several μm. It isnecessary for the membrane to not be damaged by the differentialpressure for separating atmospheric pressure and the vacuum. Thus, anarea of the membrane 10 has an area with a maximum size of approximatelyseveral tens of μm to several mm at largest. A shape of the membrane 10may be a rectangular and the like in addition to a square. The shape isarbitrary. A base for manufacturing the membrane 10 is silicon and if amembrane material is formed as a film on silicon and then wet etching isprocessed, areas are different in an upper portion and a lower portionof the membrane as illustrated in the view. That is, an opening area ofthe base 9 on the upper side is greater than the membrane area in theview.

The base 9 supporting the membrane 10 is provided on a membranemaintaining member 155. Although not illustrated, the base 9 and themembrane maintaining member 155 are adhered by O-ring, gasket, adhesive,double-sided tape, and the like by which vacuum seal can be performed.The membrane maintaining member 155 is fixed to a lower surface of thehousing 7 via a vacuum sealing member 124 to be detachable. Since themembrane 10 is very thin the thickness of which is approximately severalnm to several μm on the request to cause the charged-particle beam totransmit the membrane, the membrane may be damaged due to temporaldeterioration or during observation preparation. In addition, since themembrane 10 and the base 9 supporting the membrane 10 are small, directhandling is very difficult. Thus, as the example, the membrane 10 andthe base 9 are integrated with the membrane maintaining member 155 andthe base 9 can be handled via the membrane maintaining member 155without direct handling. Thus, handling (particularly, replacement) ofthe membrane 10 and the base 9 becomes very easy. That is, if themembrane 10 is damaged, the membrane maintaining member 155 may bereplaced. Even if the membrane 10 has to be directly replaced, themembrane maintaining member 155 is removed to an outside of theapparatus and the base 9 that is integrated with the membrane 10 can bereplaced on the outside of the apparatus.

In addition, although not illustrated, an optical microscope that isable to observe the sample may be disposed just under the sample 6 or inthe vicinity of the sample 6. In this case, the membrane 10 ispositioned on an upper side of the sample and the optical microscopeobserves the sample from below the sample. Thus, in this case, thesample stage 52 is necessary to be transparent with respect to light ofthe optical microscope. As a transparent material, there are transparentglass, transparent plastic, a transparent crystal body, and the like. Asmore general sample stage, there is a transparent sample stage such asslide glass (or preparation) and dish (or petri dish).

In addition, a temperature heater, a voltage applying section that isable to generate an electric field in the sample, and the like may beprovided. In this case, it is possible to observe an aspect in which thesample is heated or cooled and an aspect in which the electric field isapplied to the sample.

In addition, the membrane may be disposed two or more. For example, themembrane may be provided on the inside of the charged-particle opticalcolumn 2. Otherwise, a second membrane is provided below a firstmembrane separating the vacuum and the atmosphere and the sample may beincluded between the second membrane and the sample stage. In this case,the invention may be applied described below when the second membraneapproaches the first membrane.

In addition, an environmental cell, which can be introduced into aninside of a vacuum device in a state where the entirety of the sample isincluded, may be provided as the sample. For example, a sample heightadjustment mechanism is included in an inside of the environmental celland the invention described below can be applied even if the sampleapproaches the membrane separating the vacuum and the atmosphere. In theinvention, the number and type of the membrane are not limited andbelong to the category of the SEM or the charged-particle beam apparatusof the example, as long as they fulfill the intended function in theexample.

In addition, although not illustrated, a detector that detects thecharged-particle beam transmitting the sample 6 may be disposed justbelow the sample 6. The detector is a detection element that can detectand amplify the approaching charged-particle beam with energy of fromseveral keV to several tens of keV. For example, a semiconductordetector that is made of a semiconductor material such as silicon, ascintillator that can convert a charged-particle signal into a light ona glass surface or an inside thereof, a luminescent light emittingmaterial, a yttrium aluminum garnet (YAG) element, and the like areused. An electrical signal or an optical signal from the detector istransmitted to the control system configured of the upper controlsection 36 or the lower control section 37 via wiring, a lighttransferring path, a light detector, or the like. It is possible todetect a transmission charged-particle signal in the transmissioncharged-particle beam from the detector on which the sample is directlymounted. The detector on which the sample 6 is mounted approaches themembrane 10 separating the vacuum from the atmosphere and thereby it ispossible to acquire a transmission charged-particle beam image of thesample 6 in the atmosphere. In this case, in an approaching method ofthe sample 6 on the detector and the membrane 10, a method describedbelow can be applied.

The sample stage 5 disposed under atmosphere pressure is provided in alower portion of the membrane 10 included in the housing 7. A Z-axisdriving mechanism having a height adjusting function that is able tocause at least the sample 6 to approach the membrane 10 is provided inthe sample stage 5. Of course, an X-Y driving mechanism moving in adirection of a sample surface may be provided. Moreover, although notillustrated, as a mechanism that adjusts the distance between the sample6 and the membrane 10, a driving mechanism that drives the membrane 10and the membrane maintaining member 155 in a direction of the sample(upward and downward direction in the view) may also be provided inaddition to or instead of the Z-axis driving mechanism moving the sample6. Those mechanisms changing the distance between the membrane and thesample by moving the membrane or the sample are collectively referred toas the distance adjustment mechanism.

In the example, energy E when the charged-particle beam reaches thesample from the charged-particle beam source 8 is set and controlled. Anirradiation energy control section 59 is provided between the lowercontrol section 37 and the charged-particle optical column 2. Theirradiation energy control section 59 is a high voltage power supply andthe like that is able to change at least two conditions of theirradiation energy E of the charged-particle beam to the sample bychanging a voltage supplied, for example, to the charged-particle beamsource 8. The irradiation energy control section 59 may be provided onthe inside of the lower control section 37. In addition, as anotherexample, the irradiation energy control section 59 may be an electrodethat changes an acceleration voltage of the charged-particle beam fromthe charged-particle beam source or a power supply that variablycontrols a voltage to an optical lens that is able to accelerate ordecelerate the charged-particle beam before the charged-particle beam isapplied to the sample. As still another example, it may be a powersupply that can apply a voltage to the sample stage. Such a controlsystem may also be provided on the inside of the lower control section37 or may be provided between the lower control section 37 and theoptical lens 1. In addition, a specific example of the irradiationenergy control section of the charged-particle beam described above maybe used in combination appropriately.

<Principle Description>

A principle used to obtain a positional relationship between the sampleand the membrane, by enabling setting the irradiation energy of theprimary charged-particle beam to at least two levels of irradiationenergy, and a result thereof will be described below. In the followingdescription, the irradiation energy of the primary charged-particle beamis E1 when adjusting the distance between the membrane and the sample,and the irradiation energy of the primary charged-particle beam is E2when acquiring an observation image by scanning the sample with theprimary charged-particle beam. Moreover, as described below, even whenadjusting the distance between the membrane and the sample, imageacquisition is performed. In a case of an image for adjusting, a lowimage quality may be provided as described below, and it is sufficient,as long as it has image quality capable of acquiring parameters. On theother hand, an image that is acquired during observation is an imagethat is an object to be observed ultimately, or stored by a user, and isgenerally desired to be high quality.

First, a beam diameter D when the charged-particle beam reaches thesample will be described with reference to FIG. 2. As illustrated inFIG. 2(a), if the membrane 10 is not present and a space in which thesample is mounted is in the vacuum state, a primary charged-particlebeam 201 reaches the sample 6 in a state where the primarycharged-particle beam 201 is focused by a charged-particle opticalsystem such as the optical lens 1 and the like. In this case, when thebeam diameter of the primary charged-particle beam 201 is D0, the beamdiameter D0 is determined by lens aberration of the optical lens 1 andthe like. On the other hand, as illustrated in FIGS. 2(b) to 2(e), ifthe space in which the sample is mounted is a gas atmosphere such asthat of atmospheric pressure, the beam diameter when the primarycharged-particle beam 201 reaches the sample depends on a distance Zbetween the membrane 10 and the sample 6, and the irradiation energy E.

FIG. 2 (b) illustrates a case where the charged-particle beam is appliedto the sample 6 by the irradiation energy E1 when the distance from themembrane 10 is Z1, FIG. 2(c) illustrates a case where thecharged-particle beam is applied to the sample 6 by the irradiationenergy E1 when the distance from the membrane 10 is Z2, FIG. 2(d)illustrates a case where the charged-particle beam is applied to thesample 6 by the irradiation energy E2 when the distance from themembrane 10 is Z1, and FIG. 2(e) illustrates a case where thecharged-particle beam is applied to the sample 6 by the irradiationenergy E2 when the distance from the membrane 10 is Z2. In addition, thefollowing Expressions are satisfied between E1 and E2, and Z1 and Z2.

E1<E2  (Expression 1)

Z1>Z2  (Expression 2)

In FIG. 2(b), the irradiation energy E1 is relatively small and thedistance Z1 is relatively long. Thus, the charged-particle beam isscattered by the atmosphere or gas under a desired gas pressure betweenthe membrane 10 and the sample 6 until the charged-particle beam reachesthe sample 6 and the beam diameter is greater than D0 as indicated by D1of the view. If a size of the observation object of the sample 6 issmaller than the beam diameter D1, the observation object cannot beidentified in the image. In FIG. 2(c), the distance between the membrane10 and the sample 6 is shortened to Z2, since the number of times orprobability that the charged-particle beam is scattered by theatmospheric pressure or gas under a desired gas pressure is reduced, thebeam diameter D2 can be smaller than D1. As a result, the observationobject of the sample 6 can be identified in the image. That is, if thedistance between the membrane 10 and the sample 6 is closer as much aspossible, it is possible to increase resolution of the image. On theother hand, in FIG. 2(d), since the irradiation energy E2 of a primarycharged-particle beam 202 is relatively large, even if the distancebetween the membrane 10 and the sample 6 is Z1, a beam diameter D3 ofthe primary charged-particle beam 202 can be in a state of being smallcompared to D1. Thus, even in a case of the distance Z1, the observationobject of the sample 6 can be identified in the image. In addition, asillustrated in FIG. 2(e), if the distance between the membrane 10 andthe sample 6 is shortened to Z2, the beam diameter can be a beamdiameter D4 that is further small and it is possible to observe thesample 6 in resolution higher than that of the case of FIG. 2(d).

That is, if the irradiation energy E is high, the observation object ofthe sample 6 can be identified even if the distance Z is great, but ifit is desired that the observation is performed in higher resolution,the distance between the membrane 10 and the sample 6 is preferablyshortened. As described above, if the distance between the membrane 10and the sample 6 is shortened as much as possible, the image qualitybecomes improved.

When considering the viewpoint described above, if observation isperformed only in the irradiation energy E2, it may be said that it isdifficult to recognize whether or not the distance between the membrane10 and the sample 6 is in a certain degree based on the charged-particlebeam image. That is, if observation is performed with the irradiationenergy E2, there is a problem that distance is not ascertained. If thesample 6 approaches the membrane 10 in the sample stage 5 in a statewhere the distance between the membrane 10 and the sample 6 is notknown, the sample 6 excessively approaches the membrane 10 and comesinto contact with the membrane 10, and, as a result, the membrane 10 maybe damaged.

Next, a case where secondary charged-particles reach the detector 3 fromthe sample will be described with reference to FIG. 3. The primarycharged-particle beam reaching the sample 6 causes the secondarycharged-particles such as reflected charged-particles or secondcharged-particles to be generated, the secondary charged-particles reachthe detector 3, and thereby the secondary charged-particles are detectedas a microscope image. The secondary charged-particles capable ofreaching the detector 3 via the air space and the membrane 10 are thecharged-particle beam that maintains high energy, that is, thecharged-particle beam that is elastically scattered or slightlyinelastically scattered. When energy of an incident charged-particlebeam is E and energy of the secondary charged-particles is E′, thefollowing is satisfied.

E′≅E  (Expression 3)

That is, as the incident energy E is increased, the energy E′ of thesecondary charged-particles is also increased. As illustrated in FIG.3(a), a case where the membrane 10 is not present and the space in whichthe sample is mounted is in the vacuum state may be considered. In thiscase, secondary charged-particles 203 reach the detector 3 without beingscattered. An amount of the secondary charged-particles reaching thedetector is B0. In this case, the secondary charged-particles emittedfrom the sample can reach the detector 3 without being scattered becausea vacuum is present between the sample 6 and the detector 3.

On the other hand, as illustrated in FIGS. 3 (b) to 3(e), if the spacein which the sample is mounted is a gaseous atmosphere such as that ofatmospheric pressure, the amount of secondary charged-particles 203reaching the detector 3 depends on the distance between the sample 6 andthe membrane 10. FIG. 3(b) illustrates a case where the charged-particlebeam is applied to the sample 6 of which the distance from the membrane10 is Z1 by the irradiation energy E1, FIG. 3(c) illustrates a casewhere the charged-particle beam is applied to the sample 6 of which thedistance from the membrane 10 is Z2 by the irradiation energy E1, FIG.3(d) illustrates a case where the charged-particle beam is applied tothe sample 6 of which the distance from the membrane 10 is Z1 by theirradiation energy E2, and FIG. 3(e) illustrates a case where thecharged-particle beam is applied to the sample 6 of which the distancefrom the membrane 10 is Z2 by the irradiation energy E2. Here, therelationships indicated by (Expression 1) and (Expression 2) aresatisfied between E1 and E2, and Z1 and Z2. In FIG. 3(b), theirradiation energy E1 is relatively small and the distance Z1 isrelatively long. Thus, until the secondary charged-particles reach thedetector 3, the secondary charged-particles are scattered by gas underatmosphere or a desired gas pressure between the membrane 10 and thesample 6, and an amount B1 of the secondary charged-particles thatactually reach the detector 3 is smaller than B0. For example, thesecondary charged-particles emitted from the sample are also scatteredin a direction other than the direction of the membrane 10 and thedetector 3. Furthermore, a beam receiving inelastic scattering by gasunder atmospheric pressure or a desired gas pressure between themembrane 10 and the sample 6 is also included in the amount B1 of thesecondary charged-particles. For these reasons, the energy E′ of thesecondary charged-particles reaching the detector 3 is decreased and theamount of the secondary charged-particles of the energy E that areelastically scattered is decreased to less than B1. Sensitivity or theamplification rate of the detector 3 such as the semiconductor elementor the scintillator for detecting the charged-particle beam generallydepends on energy of the incident charged-particle beam. As a result, ifthe microscope image of the sample 6 is acquired in a state of FIG.3(b), brightness of the detected image becomes very dark compared toFIG. 3(a). The reason is that the number of the secondarycharged-particles reaching the detector 3 is decreased by beingscattered by gas under the atmosphere or a desired gas pressure and theamplification rate of the detector 3 is reduced.

On the other hand, as illustrated in FIG. 3(c), when decreasing thedistance between the membrane 10 and the sample 6 to Z2, the number oftimes or probability to be scattered by gas under atmospheric pressureor a desired gas pressure is reduced. Thus, it is possible to increasethe amount B2 of the detected secondary charged-particles more than B1.As a result, it is possible to recognize that the sample 6 approachesthe membrane by the brightness of the image. In FIG. 3(d), since theirradiation energy E2 of the primary charged-particle beam 202 isrelatively large, even if the distance between the membrane 10 and thesample 6 is Z1, the amount B3 of the secondary charged-particles is in astate of being greater than B1. In addition, as illustrated in FIG.3(e), if the distance between the membrane 10 and the sample 6 isdecreased to Z2, since the secondary charged-particles B4 can be greaterthan B3, the image of the sample 6 can be clearer.

When considering the viewpoint described above, if the irradiationenergy E is high, even if the distance Z is changed, the secondarycharged-particles can reach the detector 3 from the sample 6, it may besaid that the distance Z is difficult to be obtained based on the image.On the other hand, if it is desired to perform the observation at ahigher resolution and the like, the image quality is improved as thedistance between the membrane 10 and the sample 6 is as close aspossible. Thus, it is preferable that the distance between the membrane10 and the sample 6 is short. Thus, as described above with reference toFIG. 2, also for the secondary charged-particles, if the observation isperformed only by the irradiation energy E2, it is difficult torecognize whether the distance between the membrane 10 and the sample 6is a certain degree based on the charged-particle beam image. That is,in a state where the distance between the membrane 10 and the sample 6is not known, if the sample 6 approaches the membrane 10 in the samplestage 5, the sample 6 excessively approaches the membrane 10 and comesinto contact with the membrane 10, and, as a result, the membrane 10 maybe damaged.

Then, in the example, in a state of the irradiation energy E1, only acase where the distance between the membrane 10 and the sample 6 issufficiently close utilizes that the observation object of the sample 6can be identified. That is, in a state of the irradiation energy E1,image acquisition is started (FIG. 2(b) or 3(b)). Next, the distancebetween the membrane 10 and the sample 6 is gradually shortened and ifthe observation object of the sample 6 is identified, (FIG. 2(c) or3(c)), it changes to E2 that is a stronger irradiation energy, and theobservation is performed at a higher resolution (FIG. 2(e) or 3(e)). Asa result, it is possible to make the sample very simply approach themembrane compared to a method of shortening the distance between themembrane 10 and the sample 6 only with the image acquired by theirradiation energy E2.

The above description will be described in detail with reference to FIG.4. FIG. 4(a) illustrates a relationship between the distance Z betweenthe membrane and the sample and signal brightness B. FIG. 4(b)illustrates a relationship between the distance Z between the membraneand the sample and image resolution D. The image resolution D is anamount corresponding to the beam diameter and in the followingdescription, the image resolution and the beam diameter may be handledas an equal parameter. In a case of the irradiation energy E2, if thedistance is close, the signal brightness B and the image resolution (orthe beam diameter) D are gradually reduced (curve indicated by a dottedline in the view). In a case of the irradiation energy E1, if thedistance between the membrane and the sample is not sufficiently close,the signal brightness B and the image resolution (or the beam diameter)D are not improved. In the example, with the use of the principle thedistance between the membrane and the sample is adjusted by using apoint in which the image quality of the image acquired in the state ofthe irradiation energy E1 is sharper. The point, at which the imagequality is sharper, is a point at which a shape or a surface shape ofthe sample 6 begins to appear sharp because the number of times that theprimary charged-particle beam is scattered is very low, that is, a sizeof the shape configuring the sample 6 and the beam diameter of theprimary charged-particle beam substantially match each other. Asillustrated in FIG. 4, since signal brightness or the image resolutionwith respect to the distance between the membrane and the sample iscontinuously changed, if the membrane and the sample are continuouslyclose, a detection rate of the signal due to the sample is precisely andcontinuously changed. However, also in this case, as described belowwith reference to FIGS. 5 to 7, a threshold of the signal brightness orthe image resolution, with which a user or a computer can recognize theshape of the sample in the image, is present. The threshold is expressedas the point at which the image is sharply better. For example, ifdetermination is performed by the computer, it is the point in which theimage is sharper in a state where a significant amount of the signal dueto the sample is detected with respect to a signal of a background. Inaddition, if the distance between the membrane and the sample isstepwise close, the sample image cannot be recognized in a certaindistance Z1 and a state where the sample image can be recognized ispresent in Z2 that is closer than Z1. In this case, the point in whichthe image quality is sharper means a state corresponding to Z2.

That is, the point in which the image quality is sharply better is thethreshold (signal brightness: Bz and the image resolution Dz) and thenapproaching of the sample and the membrane is performed until thethreshold is reached. That is, when the sample and the membrane beingpositioned at a separated position is a 0 point, the distance Z betweenthe membrane and the sample is close until the signal brightness or theimage resolution becomes a certain threshold (signal brightness: Bz andthe image resolution Dz in the view). A state where the distance isclose to reach the threshold is indicated as the P point in the view. Inthis state, if the irradiation energy is changed from E1 to E2 whilefixing the distance Z, the signal brightness B and the image resolutionD are in a state of being indicated by a Q point in the view and theimage quality is significantly improved.

More specifically, a case where E1 is 5 kV and E2 is 15 kV will bedescribed. In addition, the distance between the membrane and the sampleat the 0 point is 50 μm. In a theoretical calculation result of a meanfree path (distance that can precede without colliding with anatmospheric component) in which the charged-particle beam is theelectron beam and air component is considered to be present 1 atmbetween the membrane and the sample, the mean free path of the electronbeam is approximately 15 μm when the irradiation energy is 5 kV and themean free path of the charged-particle beam is approximately 50 μm whenthe irradiation energy is 15 kV. That is, when the irradiation energy E1is 5 kV, if the distance between the membrane and the sample is reducedfrom 50 μm that is the 0 point to approximately 15 μm or less that isthe mean free path in 5 kV, it reaches the P point in which the imagequality is sharper and the image of the sample is started to be lookedat. Thereafter, if the irradiation energy is changed to 15 kV, in astate where the distance between the membrane and the sample is 15 μm,it is possible to irradiate the sample with the electron beam by theirradiation energy of 15 kV in the mean free path of 50 μm. Thus, itreaches the Q point in which the image quality is further improved andit is possible to obtain the image in which scattering of thecharged-particle beam is considerably reduced.

Here, an aspect that determination of whether or not the threshold isreached is obtained from an image change will be described withreference to FIG. 5. Moreover, as illustrated in FIG. 5, the brightnessinformation or the resolution information described above can also beobtained from a profile of the detection signal or the brightness or theresolution can also be obtained by the image that is generated from thedetection signal. Thus, parameters such as the brightness, theresolution, and the like for monitoring the distance between themembrane and the sample may be directly acquired from the detectionsignal or may be recognized from the image. FIG. 5(a 1) is a schematicsectional view in a case where the distance between the membrane 10 andthe sample 6 is Z0, FIG. 5(a 2) is an explanatory view of the microscopeimage acquired by the detector 3 in FIG. 5(a 1), and FIG. 5(a 3) is aline profile of image brightness of line A of FIG. 5(a 2). FIGS. 5(a) to5(c) are an example in which irradiation is performed by the irradiationenergy E1 and FIG. 5(d) is an example in which irradiation is performedby the irradiation energy E2 that is greater than E1.

In a case where the distance between the membrane 10 and the sample isZ0 that is relatively large, since the secondary charged-particles arenot returned from a lower surface of the membrane 10, as illustrated inFIG. 5(a 2), the membrane 10 portion appears dark in the image and onlythe secondary charged-particles from the base 9 are acquired by thedetector 3. Thus, as illustrated in FIG. 5(a 2), a base 9′ in an upperregion of the membrane 10 is observed as the microscope image. Inaddition, in this case, the line profile is formed as illustrated inFIG. 5(a 3).

Next, as illustrated in FIG. 5(b 1), if the distance between themembrane 10 and the sample 6 is Z1 that is closer than Z0, the secondarycharged-particles are returned from the lower surface of the membrane 10to some extent. Thus, as illustrated in FIG. 5(b 2), the microscopeimage of the sample 6 can recognize that the sample 6 is present belowthe membrane 10. However, as illustrated in FIG. 2, since the beamdiameter is large and the secondary charged-particles reaching thedetector 3 are small, as illustrated in the line profile of FIG. 5(b 3),the microscope image of the sample 6 is looked at to an extent ofblurred dark. This is indicated by a signal 6 b. Next, as illustrated inFIG. 5(c 1), in a case where the distance between the membrane 10 andthe sample 6 is Z2 that is closer than Z1, the secondarycharged-particles are incident on the sample 6 in a state where the beamdiameter is small and most of the secondary charged-particles aredetected by the detector 3. Thus, the microscope image of the sample 6is provided as illustrated in FIG. 5(c 2) and it is possible to observethe microscope image of the sample 6 over the membrane 10. Also in FIG.5(c 3) of the line profile of the image brightness of the line A, thesample 6 can be looked at to some extent. Finally, if the irradiationenergy is E2 while maintaining the positional relationship between themembrane and the sample of FIG. 5(c 1), as described above, the beamdiameter is further reduced when reaching the sample 6 and the secondarycharged-particles reaching the detector 3 are further increased. Thus,as illustrated in FIGS. 5(d 2) and 5(d 3), the signal of the sample 6 isa signal 6 d and it is possible to very slowly perform the observation.That is, as the image is in the state of FIG. 5(c 2) and the lineprofile is in the state of FIG. 5(c 3), if a state where the observationobject is looked at in the image is identified in the state of theirradiation energy E1, it is possible to determine that the distancebetween the membrane 10 and the sample 6 is in a state of approaching toZ2 that is an appropriate distance for the observation.

More specifically, if the irradiation energy is approximately from 1 kVto 50 kV, the irradiation energy E and the mean free path λsubstantially satisfy the following relationship.

λ∝E  (Expression 4)

That is, if the irradiation energy E is three times, the mean free pathis substantially three times. In the example, in order to execute amethod of changing the irradiation energy E, it is preferable that aratio between E1 and E2 is large as much as possible and, for example,the E2/E1 ratio may be approximately 2 times or more. That is, an energyratio directly corresponds to a distance ratio between the membrane andthe sample, and then a sample height may be adjusted in a distanceapproximately half of the mean free path of E2.

The line profile and the threshold (signal brightness Bz and the imageresolution Dz) will be described with reference to FIGS. 6(a) to 6(c).Each distance between the sample 6 and the membrane 10 from FIGS. 6(a)to 6(c) corresponds to each of FIGS. 5(a) to 5(c). when ends of themembrane are X1 and X2, a region to be monitored within the line profileis a signal change corresponding to the brightness B and the imageresolution D between X1 and X2 (between X1-X2). Since the member 9maintaining the membrane is observed from the vacuum side (signal 9′ inthe view), the charged-particle beam is not scattered by the atmosphericcomponent. Thus, if the sample 6 is not present below the membrane 10,the distance is substantially away from each other, or the like, asignal amount of a signal from the base 9 is greater than signalstrength B between X1 and X2. When a signal amount from the member 9maintaining the membrane is B0 and a signal amount between X1 and X2 isB, the signal amounts are as illustrated in FIG. 6(a). If the distancebetween the membrane 10 and the sample 6 is close, the signal strengthbetween X1 and X2 is increased. Here, a threshold Bz is set in a certainconstant signal amount. That is, the sample 6 approaches the membrane 10until a state where the signal strength B reaches Bz by observing andmonitoring whether the signal strength B between X1 and X2 reaches Bz.In addition, it may also be monitored when reaching a value ΔB that is adifference between B0 and B. For example, if the brightness building theimage is formed with 256 gradations (that is, a case where it isdigitalized in which the brightest signal is 256 and the darkest signalis 1), if B0 is brightness of 200 gradations and an initial value of Bis brightness of 100 gradations, Bz may be 180. In addition, it may bemonitored when a value ΔB that is obtained by subtracting B from B0 is20. Moreover, when the brightness building the image is 256 gradations,if the signal amount B0 from the member 9 maintaining the membrane isset to be 256 or more or the signal strength B between X1 and X2 is setto be 1 or less, correct Bz or ΔB cannot be acquired or monitored. Thus,if brightness building the image is 256 gradations, the distance betweenthe membrane and the sample is whatever, the brightest signal has to be256 and the darkest signal has to be 1.

Next, a method of observing or monitoring a change in the imageresolution D between X1 and X2 will be described. The image resolution Dcorresponds to a spreading width of the signal due to the sample. Thus,a state where the width of the signal due to the sample becomes apredetermined threshold Dz is recognized or monitored. Dz is a size ofan object or half the size of the object that is identified whencontrast of the detection signal becomes the maximum. That is, it is adistance from the minimum to the maximum of a line profile signal.Moreover, in setting of the threshold Dz, a ratio with respect to thesize of the object is arbitrarily changeable, or the spreading width maybe directly designated instead of the ratio with respect to the size ofthe object. As illustrated in FIGS. 6(b) and 6(c), if the sample and themembrane approach together, the signal B due to the sample is detectedbetween X1 and X2. A state where the width of the signal due to thesample detected between X1 and X2 becomes Dz may be recognized ormonitored. In addition, as another method, the signal between the lineprofiles is performed by Fourier transform and is converted intofrequency characteristics, and then a position which becomes a specificfrequency fz may be recognized. A state where resolution of the signaldue to the sample becomes a certain threshold is determined as a statewhere the distance between the sample 6 and the membrane 10 becomes Z2.

As described above, it is possible to identify the distance between thesample 6 and the membrane 10 by comparing the line profile to thethreshold (signal brightness Bz and the image resolution Dz) byobserving or monitoring the line profile. In addition, as anothermethod, the distance between the sample 6 and the membrane 10 isnon-contact as long as it is equal to or less than the threshold andthereby observation may be performed without contacting the sample withthe membrane. In other words, as described in Example 2 in detail, thethreshold can use to alert to the effect that there is a risk that themembrane and the sample come into contact with each other.

Moreover, the above description is given that both the Bz and Dz areobserved or monitored, but it may be either one. For example, if thesample 6 is completely flat, the brightness B becomes large, but achange of the image resolution D may not be observed. In this case, onlyBz may be observed or monitored.

In addition, in a case of the reflected charged-particles that arereflected and returned by elastically scattering or inelasticallyscattering of the secondary charged-particles returning from the sample6 to the membrane 10 side, the signal amount detected by the detector 3depends on an atomic weight of the sample 6. For example, if the base 9in a periphery of the membrane 10 is silicon and the sample 6 is goldand the like, since the atomic weight of the sample 6 is greater thanthat of the base 9, as illustrated in FIGS. 7(a) to 7(c), when thedistance between the membrane 10 and the sample 6 is short, the signalamount of a signal 6 c of the sample 6 is greater than the signal amountfrom the member or the base 9 maintaining the membrane. Thus, thethreshold Bz or ΔB to be recognized or monitored is necessary to beconsidered depending on a material wanted to be looked at. Conversely,if the material wanted to be looked at is known, it is known that thebrightness B becomes a certain degree if whether the distance is formedin a certain degree. Since this is known, as illustrated below in FIG.10, in a state where the membrane 10 is not present, brightness of thematerial that is the observation object is acquired in advance and thenmay also be registered or stored as data.

In addition, whether a certain material becomes certain brightness isslightly different by the apparatus configuration such as the positionalrelationship between the material and the detector. Thus, as illustratedin FIG. 3(a), in a state where the membrane 10 is not present by theapparatus configuration, the distance between the material and thedetector is made to be constant and then the difference in thebrightness may be acquired depending on the material by putting variousmaterials into the apparatus.

<Procedure Description>

As described above, the principle, in which the distance between themembrane and the sample is shortened until reaching a certain threshold(signal brightness: Bz and the image resolution Dz) by the irradiationenergy E1, and then the distance between the membrane and the sample canbe adjusted by observing the image by the irradiation energy E2, isdescribed. Hereinafter, a procedure that performs the image acquisitionby controlling the irradiation energy E and the distance Z between themembrane 10 and the sample 6 will be described with reference to FIG. 8.Initially, in step 300, the sample to be observed is disposed on asample table or the sample stage 5. Next, in step 301, the sample 6 isdisposed under the membrane 10. Next, the irradiation energy E1 of theprimary charged-particle beam is set (step 302) and then an output ofthe microscope image is executed by starting beam irradiation (step303). Adesired image brightness and a focus are set in the membrane 10portion or a peripheral portion thereof (step 304). Finally, since thesample 6 is close to the vicinity of the membrane 10, the edges X1 andX2 of the base 9 included in the membrane 10 may be focused. Asdescribed above, the sample 6 comes to the vicinity of the membrane 10and if the sample 6 comes within a depth of the focus, the focus isautomatically fit to the sample 6. Next, in step 305, the threshold(signal brightness Bz and the image resolution Dz) is set. A desiredimage brightness and the threshold of the image resolution may be storedby the user of the apparatus or as described below, may be set on acomputer. When setting on the computer, the desired image brightness andthe threshold of the image resolution can be automatically operated bythe control section. The threshold is a predetermined value Bz of thebrightness of the image or is a signal change corresponding to the imageresolution Dz. Next, the membrane 10 and the sample 6 approach togetherby moving the sample stage 5 (step 306). Next, in the acquired image orprofile, whether brightness of the sample over the membrane 10 or theimage resolution reaches the threshold is monitored. The operation maybe executed by the user visually or as described below, may beautomatically monitored by the computer. If it does not reach thethreshold, approaching of the membrane 10 and the sample 6 is continued.If it reaches the threshold, whether the distance between the membraneand the sample is a predetermined distance or a distance equal to orless than the predetermined distance is detected or recognized, andapproaching of the membrane 10 and the sample 6 is stopped (step 308).In a case where determination on whether or not it reaches the thresholdis automatically performed, if a message indicating that it reaches thethreshold is displayed on a screen of the computer 35, the user easilygrasps the message. Next, the irradiation energy is set to E2 whilemaintaining the distance between the membrane 10 and the sample 6 (step309). Finally, the image is acquired from the detection signal obtainedfrom the sample by applying the primary charged-particle beam of theirradiation energy E2 and the observation is executed (step 310). Asdescribed above, a method, in which the membrane 10 and the sample 6approach together while remaining the irradiation energy E1 constant,and the observation is executed by the irradiation energy E2, isdescribed. However, as described in process 311 in the view, afterobservation is performed by the irradiation energy E2, it may bereturned to the observation process 302 of the irradiation energy E1again. In addition, if the image is acquired satisfactorily only by theirradiation energy E1, the image acquisition for the observation may beperformed after step 308 as it is.

In the example, the method of approaching the distance between themembrane and the sample by grasping the positional relationship betweenthe membrane and the sample by changing the irradiation energy can beexecuted regardless of the shape of the membrane, the shape of the basesupporting the membrane, and the like.

The above description is given to recognize the distance Z by changingthe irradiation energy E. Hereinafter, one method of recognizing thedistance Z by using the image acquired by irradiation of thecharged-particle beam or the brightness profile information of the imagewill be described. An apparatus configuration is similar to theconfiguration of FIG. 1. However, in the apparatus using in the method,the membrane is provided on the sample side from the detector detectingthe secondary charged-particles. In addition, the membrane is maintainedon the base made of a material that shields, reflects, or scatters thecharged-particle beam and the periphery of the membrane is surrounded bythe base. Hereinafter, the “edge of the membrane” indicates a boundaryportion between the membrane and the base or a region in the vicinitythereof. In the method, the distance between the membrane and the sampleis recognized by using a phenomenon in which the brightness of the imageis changed by the position by a size between X1-X2 of the membrane 10, asize of the detector, or a positional relationship thereof. Imageformation will be described in detail with reference to FIG. 9. Asillustrated in FIG. 9(a 1), the detector 3 is an annular type detector600 provided below the charged-particle optical column 2. The annulartype detector refers to a detector in which a hole 601 is providedbetween a detection surface 501 and a detection surface 502 in the view,through which the primary charged-particle beam on an optical axispasses.

Here, in order to simplify the description, the sample 6 is flat and isconfigured of the same material. In FIG. 9(a 1), a positionalrelationship between the base 9 and the membrane 10, and shapes thereofare illustrated. After a primary charged-particle beam 602 passes ortransmits the membrane 10, and then is applied to the sample, thesecondary charged-particles are emitted from the sample. Secondarycharged-particles 603 emitted from just below the edge X1 of themembrane or in the vicinity thereof in a direction of the detectionsurface 501 on the right side in the view reach the detection surface501 on the right side in the view of the annular detector, but if thebase 9 is present, secondary charged-particles 604 emitted in adirection of the detection surface 502 on the left side in the view areshielded by the base 9 and do not reach the detection surface 502 on theleft side in the view. Similarly, the secondary charged-particlesemitted from just below the edge X2 of the membrane or in the vicinitythereof reach the detection surface 502 on the left side in the view ofthe annular detector 600, but if the base 9 is present, secondarycharged-particles do not reach the detection surface 501 on the rightside in the view. On the other hand, secondary charged-particles 606emitted by a primary charged-particle beam 605 applied to the vicinityof an intermediate of X1-X2 are detected in either the detection surface501 on the right side and the detection surface 502 on the left side inthe view depending on the distance between the sample 6 and the membrane10. As a result, an acquired image is illustrated in FIG. 9(a 2). InFIG. 9(a 2), an upper surface portion 9′ of the base 9 maintaining themembrane 10, and the membrane portion 10 are observed. In addition, aline profile on A line of FIG. 9(a 2) is illustrated in FIG. 9(a 3).That is, a detection signal on a side close to the edge (portion bondingto the base 9) of the membrane 10 is smaller than a signal from a centerthereof and pixels of the image corresponding to the vicinity of theedge of the membrane 10 are darker than the center position of themembrane. When considering the line profile, a signal detection amountwithin a range of certain distances from the edge X1 of the membrane 10is smaller than that of the center position of the membrane. A region inwhich the signal detection amount is decreased is defined by a signalattenuation distance L. The signal attenuation distance L may bedetermined by, for example, a distance between a pixel in whichbrightness is equal to or less than a predetermined ratio with respectto the center position (in other words, a center position of the image)of the membrane and a pixel which corresponds to the edge of themembrane. In addition, as another definition, it may be a distance froman edge of the membrane of a portion having a predetermined brightnessvalue or a brightness value equal to or less than the predeterminedbrightness value. Here, the signal attenuation distance L is determinedonly by a geometric relationship. For example, only the distance Zbetween the sample 6 and the membrane 10 is changeable under conditionsthat each size of the detector 600, the membrane 10, and the base 9, apositional relationship thereof, and a thickness and an opening angle ofan upper surface and a lower surface of the base 9 are constant. Thus,the signal attenuation distance L is a function of only the distance Z.That is, when measuring the signal attenuation distance L, the distanceZ is found. Moreover, even if a brightness value of a portion having apredetermined distance from the edge of the membrane is used as aparameter instead of the signal attenuation distance L, it is possibleto monitor the distance between the membrane and the sample similar to amethod described below. For the sake of simplicity, hereinafter, anexample of the signal attenuation distance L will be described.

As illustrated in FIG. 9(b 1), if the distance Z between the membrane 10and the sample 6 is shortened to be Z4 (>Z3), the secondarycharged-particles 604, which are emitted from the vicinity of the edgeX1 in the direction of the detection surface 502 on the left side in theview, are also detected compared to the case of FIG. 9(a 1). Thus, thesignal attenuation distance L is close to 0.

In summary, if an amount of the secondary charged-particles generatedjust below the edges X1 and X2 of the membrane or in the vicinitythereof, specifically, the signal attenuation distance L obtained fromthe line profile is detected, the distance between the membrane 10 andthe sample 6 is determined. As described above, it is possible tomonitor the distance Z between the sample 6 and the membrane 10 byobserving, measuring, or monitoring the signal attenuation distance L asa parameter. More specifically, since a distribution of thecharged-particle beam that is obtained by applying and reflecting thecharged-particle beam to and on the sample is obtained in accordancewith a cos distribution, the number of the reflected charged-particlesemitted in a 45° direction is the highest number. For example, if thedetector 600 is sufficiently large and the hole 601 through which theprimary charged-particle beam passes is ignored, when an angle betweenlines connecting the irradiation beam 605 of the primarycharged-particle beam, an irradiation position of the charged-particlebeam, and the edges X1 and X2 of the membrane is equal to or less than450, the image is much darker. Conversely, if the above-described angleis equal to or greater than 450, the image is brighter and is determinedby the geometric relationship. Thus, a relationship of the distancebetween the apparatus-specified signal attenuation distance L and themembrane-the sample is constant by an area of the membrane 10, the sizeand the shape of the base 9, the size of the detector 600, the sizes andthe positions of the detection surfaces 501 and 502, and the like by theapparatus. Thus, it is possible to estimate the distance Z from theimage.

Conversely, as long as the signal attenuation distance L is observed,since the distance between the membrane 10 and the sample 6 is a certainvalue or more, it is possible to confirm that the sample 6 does not comeinto contact with the membrane 10 by monitoring the signal attenuationdistance L. Thus, it is possible to execute the observation withoutcontacting the sample to the membrane.

In addition, as described above, the amount of the secondarycharged-particles depends on the atomic weight of the sample 6. Thus, itis necessary to adjust a threshold Lz to be recognized or monitoreddepending on the material wanted to be looked at. That is, the materialwanted to be looked at is known, it is known that the brightness Bbecomes a certain degree if whether the distance is formed in a certaindegree. Thus, the threshold Lz may be adjusted depending on the materialof the sample. The adjustment of the threshold Lz may be performed bythe user via the input section of the computer 35 or may be stored by anoperation of the user himself or herself.

In addition, whether any material becomes any brightness is slightlydifferent by the apparatus configuration such as the positionalrelationship with the detector. Thus, as illustrated in FIG. 10, in astate where the membrane 10 is not present by the apparatusconfiguration, the base 9 is disposed, the distance between the detector600 and the sample 6, and the distance Z between the base 9 and thesample 6 are changed, and whether it becomes any signal attenuationdistance L depending on the distance Z may be measured in advance.Measured results may be stored in the storage section of the computer 35as functions or databases of the signal attenuation distance L withrespect to the distance Z for each material, or may be stored by theuser himself or herself. Otherwise, in a state where the distancebetween the membrane and the sample is known by causing a flat sample tocollide with a member after putting the member of which a thickness isknown between the sample and the membrane, an operation to acquire thesignal attenuation distance L may be performed by observing an image. Inthis case, if a relationship between a thickness t of theabove-described member and the signal attenuation distance L by changingthe thickness t for several times is stored in the computer 35 as atable, it is also possible to measure a very accurate absolute value ofthe distance Z.

A procedure of performing the image acquisition by controlling thedistance Z between the membrane 10 and the sample 6 by using informationof the signal attenuation distance L will be described with reference toFIG. 11. Moreover, in the process, the irradiation energy may bechangeable or may be constant. In an initial step, the sample to beobserved is disposed on the sample table or the sample stage 5 (step800). In the next step, the sample 6 is disposed under the membrane 10(step 801). Next, after an acceleration voltage is set (step 802), themicroscope image is acquired by starting beam irradiation (step 803). Adesired image brightness and a focus are set in the membrane 10 portionor a peripheral portion thereof (step 804). Finally, since the sample 6is closer to the vicinity of the membrane 10, a focus may be provided tothe edges X1 and X2 of the base 9 including the membrane 10 in step 804.Thus, the sample 6 is close to the vicinity of the membrane 10 and ifthe sample 6 comes within the depth of the focus, the focus isautomatically fit to the sample 6. In the next step, the threshold ofthe signal attenuation distance L is set (step 805). A desired imagebrightness and the threshold of the image resolution may be stored bythe user of the apparatus or as described below, may be set on acomputer and then is automatically operated. The threshold is the signalattenuation distance L. Next, the membrane 10 and the sample 6 are closetogether by operating the sample stage 5 (step 806). The signalattenuation distance L is monitored over the membrane 10 duringapproaching of the membrane and the sample and determination isperformed on whether the parameters reach the thresholds (step 807). Theoperation may be executed by the user or may be automatically monitoredon the computer described below. If the parameter does not reach thethreshold, approaching of the membrane 10 and the sample 6 is continued.If the parameter reaches the threshold or less than the threshold,approaching of the membrane 10 and the sample 6 is stopped. If amonitoring message that the parameter reaches the threshold is displayedon the monitor 33, the user easily grasps the message. For example, apredetermined threshold is set and a process that a warring is issued tothe user or moving of the sample stage is limited if the signalattenuation distance L is less than the threshold, and the like may beperformed. Setting of the threshold and the display of the warning areperformed by the computer 35. Finally, the observation is executed (step810). However, as described in step 811 in the view, if the distancebetween the sample and the membrane is not satisfied, the threshold isset again and it may be returned to step 805.

In the example, the method of approaching the distance between themembrane and the sample by grasping the positional relationship betweenthe membrane and the sample by the difference in the brightness by themembrane position is not necessary to change the irradiation energy andis able to execute approaching the sample to the membrane only by thesame irradiation energy and observation of the sample compared to themethod described above. Therefore, it is possible to execute observationwith very high throughput.

Above, the method of grasping the positional relationship between themembrane and the sample is described. That is, this indicates that thedistance between the membrane and the sample can be grasped by the imageobtained by using the charged-particle beam apparatus. Thus, accordingto the method of the example, it is possible to reduce risk of themembrane damage due to contact between the membrane and the sample.Particularly, even if there are irregularities in the sample, since theportion just below the membrane and the membrane can be actuallymonitored, it is possible to reduce risk that the sample is accidentallybumped into the membrane by measuring the interval in an incorrectlocation. In addition, according to the method of the example, it ispossible to grasp the distance between the sample and the membrane byquantitative parameters such as the brightness and resolution of theimage, and the signal attenuation distance. Thus, the distance betweenthe sample and the membrane is adjusted so that these parameters becomethe same value and thereby the distance between the sample and themembrane can be the same for each time. In addition, in order to graspthe distance between the membrane and the sample, a dedicated camera andthe like may be mounted, but according to the example, it is possible tograsp the positional relationship between the membrane and the sampleonly by using the detection principle of the charged-particle beammicroscope without mounting other components such as the camera. Thus,it is possible to inexpensively grasp the positional relationshipbetween the membrane and the sample.

Moreover, if the sample such as a soft material and a biological sampleis a soft matter, the observation may be executed when the sample comesinto contact with the membrane after the sample comes into contact withthe membrane. There is a concern that the membrane is damaged when thesample is vigorously hit the membrane even if the sample is very soft.However, after approaching of the sample and the membrane is recognizedby using the method according to the example described above, the samplecan slowly come into contact with the membrane. Thus, even if theobservation is performed by contacting between the sample and themembrane, it is useful to grasp the positional relationship between thesample and the membrane in the example.

Example 2

In the example, an apparatus automatically performing the operation, inwhich the threshold described in Example 1 is monitored and the distancebetween the membrane 10 and the sample 6 is close, will be described.Particularly, in the flow illustrated in FIG. 8, steps 306, 307, and 308are automatically executed. Otherwise, steps 806 and 807 of FIG. 11 areautomatically executed. Hereinafter, for the same portions as Example 1,description thereof will be omitted.

FIG. 12 illustrates an apparatus configuration view. A control section60 performs recognition and identification of a detection signal, andcontrol of a sample stage 5. The control section 60 is configured of adata transmitting and receiving section 400, a data memory section 401,an external interface 402, a calculation section 403, and the like. Thedata transmitting and receiving section 400 receives the detectionsignal and transmits a control signal to a stage 5. The data memorysection 401 is able to store an image signal and a line profile signal.The external interface 402 is connected to a user interface 34 such as amonitor 33, a keyboard, and a mouse, and the like. The calculationsection 403 recognizes and identifies the image signal and the lineprofile signal by performing calculation processing on the detectionsignal. As described in Example 1 and this example, the control section60 monitors the distance between the sample and the membrane based onthe signal from the detector 3 or the image generated from the signal.More specifically, the distance between the sample and the membrane ismonitored based on the brightness information or resolution informationof the detection signal or the image brightness or the resolutiongenerated from the detection signal. Specific processing contents arethe same as the description of Example 1.

The control section 60 can be realized by hardware or software. Inaddition, analog circuits and digital circuits may be mixed. Thedetection signal acquired by the detector 3 is amplified by an amplifier154 and is input into the data transmitting and receiving section 400.The data transmitting and receiving section 400 may have an AD converterthat converts an analog signal into a digital signal. In addition, astage control signal from the data transmitting and receiving section400 is transmitted to the sample stage 5 via a stage control section404. Moreover, although not illustrated, the sample 6 and the membrane10 may be close by a driving mechanism that drives the membrane 10 andthe membrane maintaining member 155 in the upward and downward directionin the view instead of approaching the sample 6 and the membrane 10 bymoving the sample stage 5 on which the sample 6 is mounted.

The threshold that is set by the monitor 33 and the user interface 34 isstored in the data memory section 401 via the external interface 402.Next, if an approaching operation between the membrane and the sample isstarted, the control signal is transmitted to the sample stage 5 and themembrane 10 and the sample 6 approach together. A signal input by thedetector 3 is input into the calculation section 403 via the amplifier154 and the data transmitting and receiving section 400, and is comparedto threshold data stored in the data memory section 401 by thecalculation section 403. For calculation processing, as described inExample 1, the brightness and the signal change of the image signal maybe used as parameters or the signal attenuation distance L may be used.When not reaching the threshold, approaching of the membrane 10 and thesample 6 is continued. When reaching the threshold, approaching of thesample is stopped. Steps 306, 307, and 308 in the flow illustrated inFIG. 8 can be automatically executed by such a configuration. Otherwise,steps 806 and 807 of FIG. 11 can be automatically executed.

FIG. 13 illustrates an example of an operation screen. Here, as theparameters and the thresholds for measuring the distance between themembrane and the sample, an example of monitoring the signal brightnessB and the image resolution D will be described.

An operation screen 700 includes a condition setting section 701, animage display section 702, a line profile display section 703, an imageadjusting section 704, a threshold setting section 705, and the like.The condition setting section 701 includes an irradiation energy Esetting section 706, an irradiation starting button 707, an irradiationstop button 708, an image storing button 709, an image reading button710, and the like. Image information and the line A that determines aline that is displayed in the line profile display section 703 aredisplayed in the image display section 702. Line profile information, abrightness threshold Bz, and a resolution threshold Dz are displayed inthe line profile display section 703. The threshold setting section 705includes a brightness threshold Bz setting section 711, a resolutionthreshold Dz setting section 712, an automatic approaching start button713, an automatic approaching stop button 714, and the like. The imageadjusting section 704 includes a focus adjusting section 715, abrightness adjusting section 716, a contrast adjusting section 717, andthe like.

The irradiation energy E setting section 706 may have a switching buttonand the like so as to simply switch two of a first irradiation energy E1and a second irradiation energy E2. The line A on the image displaysection 702 may be moved by an operation mouse, a cursor, and the like.If the line A is moved on the screen, information of the line profiledisplay section 703 is also updated depending on the position of theline A. the threshold Bz and the resolution threshold Dz are indicatedby dotted lines on the line profile display section 703, but the dottedlines are moved by the operation mouse, the cursor, and the like, andthen the threshold may also be set. In this case, the brightnessthreshold Bz setting section 711 and the resolution threshold Dz settingsection 712 are not present in the threshold setting section 705 andfigures may be updated in conjunction therewith. When observing theimage, if the focus adjusting section 715, the brightness adjustingsection 716, and the contrast adjusting section 717 of the imageadjusting section 704 are moved, the image information is updated andthe line profile information is also updated in conjunction therewith.

In addition, the line profiles may be displayed in the image displaysection 702 by being overlapped. In this case, since the line profiledisplay section 703 may be omitted, it is possible to largely displaythe image display section 702 on the screen 33.

In step 302 of FIG. 8, the irradiation energy of the primarycharged-particle beam is set in the first irradiation energy E1 by usingthe irradiation energy E setting section 706. In the process 303, theobservation is started by using the irradiation starting button 707. Adesired image is obtained by using the focus adjusting section 715, thebrightness adjusting section 716, and the contrast adjusting section 717of the image adjusting section 704. As described above, the focus may beprovided at X1 or X2 that is the edge of the base 9 including themembrane 10 by causing the sample 6 to approach the vicinity of themembrane 10. Next, the threshold of the parameter that is obtained fromthe detection signal or the image generated from the detection signalvia the brightness threshold Bz setting section 711 and the resolutionthreshold Dz setting section 712. Thereafter, the sample 6 approachesthe membrane 10 until the set threshold by pressing the automaticapproaching start button 713. The control section 60 monitors whether ornot the value of the parameter such as the brightness and the imageresolution reaches the threshold during moving of the sample 6. If thevalue of the parameter does not reach the threshold, the distanceadjustment mechanism is driven and approaching of the membrane 10 andthe sample 6 is continued. If the value of the parameter reaches thethreshold in the middle of automatic approaching, approaching of thesample is stopped. If the user forcibly stops approaching of themembrane 10 and the sample 6 in the middle of automatic approaching, itis possible to stop approaching by pressing the automatic approachingstop button 714. A message or child windows indicating that thethreshold is achieved may be displayed on the monitor 33. For example,in a case of reaching the threshold by manually operating the samplestage 5 without pressing the automatic approaching stop button 714, theuser can recognize that it reaches the threshold by displaying reachingthe threshold on the monitor 33. Thereafter, the irradiation energy E1is changed to the desired second irradiation energy E2 by using theirradiation energy E setting section 706 and then the observation ofhigh resolution is executed by application of the primarycharged-particle beam of the irradiation energy E2.

Moreover, even in a case of using the signal attenuation distance Ldescribed above, it may be set by the same operation screen. The signalattenuation distance may be used instead of the brightness and the imageresolution, or the signal attenuation distance L may be simultaneouslymonitored in combination therewith. In this case, the resolutionthreshold Dz of the threshold setting section may be substituted andanother threshold setting unit may be prepared separately. In addition,a setting field of the signal attenuation distance L may be displayed inthe threshold setting section 705. In this case, a dotted lineindicating the signal attenuation distance L is displayed on the lineprofile display section 703.

As described in the example or other examples, the charged-particle beamapparatus observing the sample under the atmospheric pressure is alsolikely to be used by a novice who is not familiar with the use of thecharged-particle beam apparatus. it is not always easy to place thesample in a position in which an optimum image can be obtained, butaccording to the example, the distance between the sample and themembrane can be adjusted automatically or semi-automatically. Thus, itis possible to achieve an effect that the sample position can beadjusted simply and accurately without damaging the membrane or thesample.

Above, in the example, the apparatus of automatically approaching of themembrane and the sample and the method thereof are described, but eachcontrol configuration, the wiring path, and the operation screen may bedisposed in portions other than the above-described portions, and thosebelong to the category of the SEM and the charged-particle beamapparatus of the example as long as those satisfy the functions intendedin the example.

Example 3

Hereinafter, apparatus configurations of a general charged-particle beamapparatus which can conveniently observe a sample under air will bedescribed. FIG. 14 illustrates an entire configuration view of acharged-particle microscope of the example. Similar to Example 1, thecharged-particle beam microscope of the example is also configured of acharged-particle optical column 2, a housing (vacuum chamber) 7supporting the charged-particle optical column on an apparatus providingsurface, a sample stage 5, and the like. Since an operation and functionof each element or additional elements added to each element aresubstantially the same as those of Example 1, detailed descriptionthereof will be omitted.

The configuration includes a second housing (attachment) 121 that isused by inserting into the housing 7 (hereinafter, first housing). Thesecond housing 121 is configured of a rectangular parallelepiped mainsection 131 and a mating section 132. As described below, at least oneside surface of rectangular parallelepiped side surfaces of the mainsection 131 is an open surface 15. Surfaces of the rectangularparallelepiped side surfaces of the main section 131 other than thesurface, in which a membrane maintaining member 155 is provided, may beconfigured of walls of the second housing 121 or may be configured ofside walls of the first housing 7 in a state where the second housing121 is incorporated in the first housing 7 without walls of the secondhousing 121 itself. The second housing 121 is fixed to an inner wallsurface or the side surface of the first housing 7, or thecharged-particle optical column. The main section 131 has a function ofaccommodating the sample 6 that is an observation object and is insertedinto an inside of the first housing 7 through the opening section. Themating section 132 configures a mating surface with an outer wallsurface on the side surface side on which the opening section of thefirst housing 7 is provided and is fixed to the outer wall surface onthe side surface side via a vacuum sealing member 126. Thus, an entiretyof the second housing 121 is fitted into the first housing 7. It is themost convenient that the opening section is manufactured by using anopening for loading and unloading the sample, which is originallyprovided in a vacuum sample chamber of the charged-particle microscope.That is, if the second housing 121 is manufactured in accordance with asize of a hole that is originally opened and the vacuum sealing member126 is mounted on a periphery of the hole, remodeling of the apparatusis necessary for only the minimum requirements. In addition, the secondhousing 121 can also be removed from the first housing 7.

The side surface of the second housing 121 is the open surface 15communicating with a surface of an air space of a size capable ofputting at least the sample in and out from the air space. The sample 6accommodated on an inside (right side from a dotted line of the view;hereinafter, referred to as a second space) of the second housing 121 isdisposed in an atmospheric pressure state during observation. Moreover,FIG. 14 is a sectional view of the apparatus in a horizontal directionwith an optical axis. Thus, only one surface of the open surface 15 isillustrated, but if the second housing 121 is vacuum-sealed by the sidesurfaces of the first housing in a depth direction and a front directionof a paper surface of FIG. 14, the open surface 15 of the second housing121 is not limited to one surface. In a state where the second housing121 is incorporated in the first housing 7, at least the opening surfacemay be one surface or more. On the other hand, a vacuum pump 4 isconnected to the first housing 7 and a closed space (hereinafter,referred to as a first space) configured of the inner wall surface ofthe first housing 7, an outer wall surface of the second housing, and amembrane 10 is able to be evacuated. In the example, it is possible toseparate a second space in a pressure manner by disposing the membraneso as to maintain a pressure of the second space to be greater than apressure of the first space. That is, a first space 11 is maintained ina high vacuum by the membrane 10 and a second space 12 is maintained inthe atmospheric pressure or a gas atmosphere of a pressure substantiallyequal to the atmospheric pressure. Thus, it is possible to maintain thecharged-particle optical column 2 and the detector 3 in a vacuum stateand to maintain the sample 6 in the atmospheric pressure duringoperation of the apparatus. In addition, since the second housing 121has the opening surface, it is possible to freely exchange the sample 6during the observation. That is, it is possible to move the sample 6 inthe air or pulling the sample 6 out or in from the apparatus while thefirst space 11 is in the vacuum state.

In a case where an entirety of the second housing 121 is fitted into thefirst housing 7, a membrane 10 is provided in a position that is justbelow the charged-particle optical column 2 on an upper surface side ofthe second housing 121. The membrane 10 is able to cause the primarycharged-particle beam emitted from a lower end of the charged-particleoptical column 2 to transmit or pass and the primary charged-particlebeam finally reaches the sample 6 through the membrane 10.

The sample stage 5 is disposed on an inside of the second housing 121.The sample 6 is disposed on the sample stage 5. The sample stage 5 isused for approaching of the membrane 10 and the sample 6. The samplestage may be manually operated or may be operated by electricalcommunication with the outside of the apparatus by providing a drivingmechanism such as an electric motor in the sample stage 5.

As described above, it is possible to observe the sample in theatmospheric pressure or the gas atmosphere by introducing attachmentincluding the membrane by using the charged-particle beam apparatus thatperforms imaging under general vacuum. In addition, since the attachmentof the example is a system to be inserted from the side surface of thesample chamber, it is easily to be large.

Also according to the apparatus configuration of the example, it ispossible to achieve the effect that the sample position can be adjustedsimply and accurately without damaging the membrane or the sample by themethod described in Examples 1 and 2.

Example 4

FIG. 15 illustrates an entire configuration view of a charged-particlemicroscope of the example. Similar to Example 3, the charged-particlemicroscope of the example is also configured of a charged-particleoptical column 2, a first housing (vacuum chamber) 7 that supports thecharged-particle optical column on an apparatus mounting surface, asecond housing (attachment) 121 that is used by being inserted into thefirst housing 7, a control system, and the like. Since an operation andfunction of each element or additional elements added to each elementare substantially the same as those of Examples 1 and 2, detaileddescription thereof will be omitted.

In a case of the charged-particle microscope of the example, it ispossible to cover an opening surface forming at least one side surfaceof the second housing 121 by a lid member 122 and to realize variousfunctions. Hereinafter, those will be described.

The charged-particle microscope of the example includes a sample stage 5as a unit for moving an observation view field by changing a sampleposition in the lid member 122. The sample stage 5 includes an X-Ydriving mechanism in a direction of a sample surface and a Z-axisdriving mechanism in a height direction. A support plate 107 formed of abottom plate supporting the sample stage 5 is mounted on the lid member122. The sample stage 5 is fixed to the support plate 107. The supportplate 107 is mounted so as to extend toward a surface of the lid member122 facing the second housing 121 and toward an inside of the secondhousing 121. Support shafts respectively extend from the Z-axis drivingmechanism and the X-Y driving mechanism, and an operation knob 108 andan operation knob 109 provided in the lid member 122 are respectivelyconnected to the Z-axis driving mechanism and the X-Y driving mechanism.The user of the apparatus adjusts the position of the sample 6 withinthe second housing 121 by operating the operation knobs 108 and 109.

The charged-particle microscope of the example includes a function ofsupplying replacement gas within the second housing or a function ofcapable of forming an air pressure state different from outside air thatis on the outside of the first space 11 or the apparatus. Acharged-particle beam emitted from a lower end of the charged-particleoptical column 2 passes through a membrane 10 via the first space thatis maintained in high vacuum and enters the second space that ismaintained in the atmospheric pressure or a low vacuum (than the firstspace). Thereafter, the charged-particle beam is applied to the sample6. In the air space, since the electron beam is scattered by gasmolecules, the mean free path is short. That is, if the distance betweenthe membrane 10 and the sample 6 is great, the primary charged-particlebeam, or secondary electrons, reflected electrons, transmissionelectrons, or the like that are generated by application of thecharged-particle beam does not reach the sample and the detector 3. Onthe other hand, scattering probability of the charged-particle beam isproportional to a mass number of and density of the gas molecules. Thus,if the second space is replaced by the gas molecules of which the massnumber is lighter than that of air or is slightly evacuated, thescattering probability of the electron beam is lowered and thecharged-particle beam reaches the sample. In addition, although not anentirety of the second space, air in at least a passing path of thecharged-particle beam in the second space, that is, between the membrane10 and the sample 6 may be replaced by gas or evacuated.

For the above reasons, in the charged-particle microscope of theexample, a mounting section (gas entering section) of a gas supply pipe100 is provided in the lid member 122. The gas supply pipe 100 isconnected to a gas cylinder 103 by a connection section 102 and then thereplacement gas enters the inside of the second space 12. A gas controlvalve 101 is disposed in the middle of the gas supply pipe 100 and aflow rate of the replacement gas flowing through the pipe can becontrolled. Thus, a signal line extends from the gas control valve 101to a lower control section 37. The user of the apparatus can control theflow rate of the replacement gas on an operation screen displayed on amonitor of a computer 35. In addition, the gas control valve 101 may beopened or closed by a manual operation.

As a type of the replacement gas, as long as gas lighter than air suchas nitrogen and steam, an effect of improving the image S/N is achieved,and for helium gas and hydrogen gas of which the mass is further light,the effect of improving the image S/N is large.

Since the replacement gas is light element gas, the replacement gas islikely to be accumulated in an upper portion of the second space 12 andis unlikely to be replaced on a lower side. Thus, an openingcommunicating with an inside and an outside of the second space isprovided on a lower side from a mounting position of the gas supply pipe100 in the lid member 122. For example, in FIG. 15, the opening isprovided in a mounting position of a pressure adjusting valve 104. Thus,since atmospheric gas is discharged from the opening on the lower sideby being pressed by the light element gas entered from a gas enteringsection, it is possible to efficiency replace the inside of the secondhousing 121 with gas. Moreover, the opening may be also served as arough exhaust port described below.

The pressure adjusting valve 104 may be provided instead of the openingdescribed above. The pressure adjusting valve 104 has a function bywhich a valve is automatically opened when an internal pressure of thesecond housing 121 becomes equal to or greater than 1 atm. A atmosphericgas component such as nitrogen and hydrogen is discharged to the outsideof the apparatus by automatically opening the pressure adjusting valveif the internal pressure is equal to or greater than 1 atm duringentrance of the light element gas. It is possible to fill the inside ofthe apparatus with the light element gas. Moreover, the illustrated gascylinder or the vacuum pump 103 may be included in the charged-particlemicroscope or the user of the apparatus may mount the gas cylinder orthe vacuum pump 103 later.

In addition, even the light element gas such as helium gas or hydrogengas, electron beam scattering may be large. In this case, the gascylinder 103 may be the vacuum pump. Then, it is possible to make theinside of the second housing be an extremely low vacuum state (that is,atmosphere of a pressure close to the atmospheric pressure) by slightlyevaporating. That is, it is possible to make a space between the firstmembrane 10 and the sample 6 be vacuum state. For example, an evacuationport is provided in the second housing 121 or the lid member 122 and theinside of the second housing 121 is slightly evacuated. Thereafter, thereplacement gas may enter. In this case, evacuation may be performed toreduce the atmospheric gas component remaining on the inside of thesecond housing 121 to be equal to or less than a predetermined amount.Thus, the high vacuum exhaust is not necessary to be performed and roughexhaust is sufficient to be performed.

In addition, although not illustrated, the cylinder 103 portion may be acomplex gas control unit and the like that are connected to the gascylinder and the vacuum pump in a complex manner. Although notillustrated, a heating mechanism for heating the sample 6 may bedisposed on the inside of the second housing 121.

In addition, an X-ray detector and a light detector are provided inaddition to the secondary electron detector and reflected electrondetector, and then EDS analysis and fluorescent beam detection may beperformed. The X-ray detector and the light detector may be disposedeither the first space 11 or the second space 12.

As described above, in the apparatus configuration, it is possible tocontrol the space in which the sample is mounted to be an arbitraryvacuum degree from the atmospheric pressure (approximately 10⁵ Pa) toapproximately 10³ Pa. In a so-called low-vacuum scanning electronmicroscope of the related art, since the electron beam columncommunicates with the sample chamber, the vacuum degree of the samplechamber is changed in association with a pressure of the electron beamcolumn if the vacuum degree of the sample chamber is lowered to be apressure close to the atmospheric pressure. However, it is difficult tocontrol the sample chamber to a pressure from the atmospheric pressure(approximately 10⁵ Pa) to approximately 10³ Pa. According to theexample, since the second space and the first space are separated fromeach other by the thin film, it is possible to freely control thepressure of the atmosphere and the gas type in the second space 12surrounded by the second housing 121 and the lid member 122. Thus, it ispossible to control the sample chamber to the pressure from theatmospheric pressure (approximately 10⁵ Pa) to approximately 10³ Pa thatis difficult to be controlled until now. Furthermore, it is possible toobserve a state of the sample not only at the atmospheric pressure(approximately 10⁵ Pa) but also continuously changing to a pressure inthe vicinity thereof. That is, the configuration of the example hascharacteristics that the second space 12 on the inside of the secondhousing is closed compared to the configuration described above. Thus,for example, gas enters between the membrane 10 and the sample 6 or thecharged-particle beam apparatus capable of evacuating can be supplied.

In the example, all the sample stage 5, the operation knobs 108 and 109,the gas supply pipe 100, the pressure adjusting valve 104, and aconnection section 310 are collectively mounted on the lid member 122.Thus, the user of the apparatus can perform operations of the operationknobs 108 and 109, replacing work of the sample, or operations of thegas supply pipe 100 and the pressure adjusting valve 104 with respect tothe same surface of the first housing. Thus, operability is greatlyimproved compared to the charged-particle microscope having aconfiguration in which configuration elements described above areindividually mounted on other surfaces of the sample chamber.

In addition to the configuration described above, a contact monitor thatdetects a contact state between the second housing 121 and the lidmember 122 is provided and may monitor that the second space is closedor opened.

Above, the apparatus of the example can observe the sample under theatmospheric pressure to a desired replacement gas type or a desiredpressure in addition to the effects of Examples 1, 2, and 3. Inaddition, it is possible to observe the sample under an atmosphere of apressure different from the first space. In addition, the SEM, which isable to observe the sample in the same vacuum state as the first spacein addition to the observation under air or a predetermined gasatmosphere by communicating the first space with the second space byremoving the membrane, is realized. Also according to the apparatusconfiguration of the example, it is possible to achieve the effect thatthe sample position can be adjusted simply and accurately withoutdamaging the membrane or the sample by the method described in Examples1 and 2.

In addition, in Example 1, the distance between the membrane and thesample is grasped by changing the irradiation energy to change the meanfree path of the charged-particle beam. In the case of this example, itis possible to cause the gas capable of changing the mean free path ofthe charged-particle beam to enter. For example, in a case of helium gasthat is the light element gas and the like, the mean free path isgreater than that of air component 10 times or more. Thus, in Example 1,the distance between the membrane and the sample may also be estimatedby changing the gas type between the membrane and the sample instead ofchanging the irradiation energy. In this case, other processes and stepsmay be similar to Example 1.

Example 5

In the example, a configuration that is a modification example ofExample 1, in which a charged-particle optical column 2 is present belowa membrane 10, will be described. FIG. 16 illustrates a configurationview of a charged-particle microscope of the example. A vacuum pump, acontrol system, and the like are omitted. In addition, a housing 7 thatis a vacuum chamber and the charged-particle optical column 2 aresupported on an apparatus installation surface by a pillar, a support,and the like. Since an operation and function of each element oradditional elements added to each element are substantially the same asthose of the examples described above, detailed description thereof willbe omitted.

As illustrated in FIG. 16(a), this apparatus includes a sample stage 5causing a sample 6 to approach a membrane 10. In apparatusconfigurations of the example, a sample surface on a lower side of thesample 6 is observed in the view. In other words, in the apparatusconfigurations of the example, an upper side of the apparatus is openedas an atmospheric pressure space. Also in this case, it is possible toadjust the distance between the membrane and the sample by the methoddescribed in Examples 1 and 2.

As illustrated in FIG. 16(b), the sample 6 may directly mount on themembrane 10 side (arrow direction). In this case, the sample stage 5 isnot necessarily required. In the example, in order to approach themembrane and the sample 6 by applying the method described in Examples 1and 2, a thickness is defined between the membrane 10 and the sample 6and a contact preventing member 56 such as a formed thin film and aremovable foil material is used. In this case, the contact preventingmember 56 is the distance adjustment mechanism described in Examples 1and 2. It is possible to safely dispose the sample 6 by providing thecontact preventing member 56. For example, a plurality of the contactpreventing members 56 having various known thicknesses are prepared.Initially, the contact preventing member 56 having a thickness t1 isdisposed on a base 9. Next, the sample 6 is mounted. The observation isexecuted by irradiation energy E1. If the distance between the sampleand the membrane is great and a desired image (or a threshold) is notobtained, the observation is executed by using the contact preventingmember 56 having a thickness t2 that is thinner than t1. Replacement isrepeatedly performed for the contact preventing member 56 having moreappropriate thickness until a desired image (or the threshold) isobtained. Finally, the observation is performed by irradiation energy E2(>E1). Thus, it is possible to execute the observation without damagingthe membrane 10 and the sample 6 by contacting therewith.

Example 6

In Example 1, the method of grasping the distance between themembrane-the sample by using the scattering principle by the aircomponent of the charged-particle beam is described. On the other hand,it is also possible to analyze a gas type and a pressure state under themembrane by the charged-particle beam using a scattering principle bythe air component of the charged-particle beam. That is, if the distancebetween the membrane-the sample, the gas type, and the pressure stateunder the membrane are also considered as a type of information of anon-vacuum atmosphere space under the membrane, it is possible toanalyze the distance between the membrane-the sample, the gas type andthe pressure state using a signal from a charged-particle detector byusing the same scattering principle. Thus, in the example, a method ofanalyzing a gas state in a non-vacuum space using the charged-particlebeam will be described. Moreover, even if the sample is not gas, it ispossible to apply the example to the sample if the sample is caused tobe the gas state by performing pre-processing such as evaporation. Sincethe example is provided to analyze the type and the pressure of gas, itcan also be called as a mass spectrometer and a type of a gas sensorthat detects presence or absence of an amount of specific gas. Theexample uses the principle greatly different from a mass spectrometerand a gas sensor of the related art in that gas is analyzed byirradiating gas that is an analysis object with the charged-particlebeam.

In order to investigate the gas type, the gas pressure, and the likepresent in a certain space, a gas mass spectrometer, a gaschromatography are generally used. These techniques analyze gas afterintroducing gas into an analysis chamber that is a vacuum space. Forexample, in the related art, an apparatus configuration that analyzesgas by ionizing gas after gas to be analyzed is introduced into thevacuum while performing differential evacuation is known.

However, in these related art, since gas is required to be in theanalysis chamber, a mechanism for introducing gas is necessary and thereis a problem that the apparatus is difficult to be small in size. Inaddition, since the sample is introduced into the analysis chamber thatis the vacuum space, if the analysis chamber is contaminated by thesample, it is necessary to clean or replace the analysis chamber. Thus,it is necessary to perform sufficient pre-processing with respect to thesample.

In order to solve the above-described problems, in the example, in anapparatus including a charged-particle beam source that generates acharged-particle beam; and a membrane through which the charged-particlebeam passes or transmits, the charged-particle beam passing andtransmitting the membrane is applied to a non-vacuum space in whichsample gas that is an analysis object is present, and a pressure or atype of gas, or presence or absence of gas, which is present in thenon-vacuum space, is analyzed based on an amount of a signal obtaineddepending on a scattering amount of the charged-particle beam.

When using the technique in the example, vacuum and air can be separatedby using the membrane, and it is possible to simply analyze presence orabsence of gas, the gas type, the gas pressure, and the like by applyingthe charged-particle beam with respect to gas that is the analysisobject over the membrane. Thus, gas is not necessary to enter theanalysis chamber that is the vacuum space.

First, an apparatus configuration, which can analyze, measure, orobserve the gas type and the gas pressure by the charged-particle beamwill be described with reference to FIG. 17. In FIG. 17, acharged-particle source 8 for emitting the charged-particle beam, acharged-particle optical column 800 including the charged-particlesource 8, and a membrane 10 are provided. An inside of thecharged-particle optical column 800 is evacuated in advance or may beevacuated by a vacuum pump (not illustrated). If evacuation can beperformed by the vacuum pump, a throttle (passing hole of thecharged-particle beam) can also be used instead of the membrane 10.Emission of the charged-particle beam from the charged-particle source 8may be performed by heating of the charged-particle beam source or maybe withdrawn by a high-voltage electrode (not illustrated). Thehigh-voltage electrode or the charged-particle source 8 may include aunit that adjusts an acceleration voltage. The inside of thecharged-particle optical column 800 may also include an optical lens 808such as the charged-particle beam microscope illustrated in Examples 1to 5. The optical lens 808 is an electromagnetic field lens and the likecapable of changing an emission state, a track, and a focus of thecharged-particle beam from the charged-particle source 8. In addition,these components are connected to a control section and operationconditions may be respectively controlled. As a detector capable ofdetecting the charged-particle beam, a detector 802 and a detector 803that is disposed in a position separated from the membrane 10 at apredetermined distance are illustrated. The detector may be one or bothdetectors. Since the number of charged-particles to be detected ischanged by a position in which the detector 803 is disposed, a positionadjusting mechanism (not illustrated) capable of adjusting the positionof the detector may be provided. Gas 804 to be analyzed is present belowthe membrane 10. Gas 804 may be analyzed in a position in which thecharged-particle optical column 800 is disposed and a gas inlet 805through which gas flows in a horizontal direction in the view may beprovided. The detector 802 or 803 is a detection element that can detectthe charged-particle beam. The detectors 802 and 803 may further includean amplifying function or an amplifier may be connected. The detectors802 and 803 are, for example, semiconductor detectors made of asemiconductor material such as silicon, a scintillator capable ofconverting a charged-particle signal into light on a glass surface or aninside thereof, and the like. A signal detected by the detector 802 orthe detector 803 is detected by a measurement instrument 806 via wiring807 and the like.

First, if the sample that is the analysis object is not gas, the sampleis gasified by performing a pre-processing such as controlling atemperature and a pressure by a gasification device provided separately.Next, the sample gas that is the analysis object is introduced into thenon-vacuum space under the membrane. Moreover, if presence or absence ofgas generation is wanted to be detected by being disposed in a portionin which gas may be generated, the gasification device described above,the gas inlet 805, and the like are not necessarily required.

Since a portion that affects scattering of the charged-particle beam isonly a space just below the membrane located on the extension of anoptical axis of the charged-particle beam, the sample may be introducedinto a local space. Thus, even if the sample is a small amount, it ispossible to analyze the sample. In other words, it is possible toanalyze the gas pressure or the gas type of a local space by the methodof the example. Moreover, here, the local space is a scale of a regionon a rectangular parallelepiped of which a height is a distance throughwhich the charged-particle beam is capable of transmitting and a bottomsurface is a membrane area. As described in Expression 4 of Example 1,the mean free path of the charged-particle beam is proportional toenergy of the charged-particle beam. For example, if the accelerationvoltage is 5 kV, the mean free path becomes approximately 15 μm under 1atm of atmosphere gas. Thus, the scale on the rectangular parallelepipeddescribed above is approximately the area of the membrane×15 μm.However, if the beam diameter of the charged-particle beam is focused bythe optical lens 808 on the inside of the charged-particle opticalcolumn 800, it is possible to analyze gas of a further small region. Forexample, if the beam of the charged-particle beam is throttled andapplied only to 1 μm², the gas analysis of a very small region of 15μm×1 μm×1 μm is performed.

The charged-particle beam that is emitted from the charged-particlesource 8 and passes through or transmits the membrane 10 is scattered bygas just below the membrane 10. Thus, the number of charged-particlesdetected by the detector 802 or the detector 803 is changed depending ona type and an amount of gas molecules present below the membrane. Forexample, if density of gas 804 present below the membrane is great,since many charged-particle beams are scattered, more charged-particlesare returned to the detector 802 as the reflected charged-particles.Thus, an output signal of the detector 802 is increased. The density ofgas is great when the pressure of gas is great or the mass number of thegas molecules is great. On the contrary, if the density of gas presentbelow the membrane is small, the charged-particle beam is not muchscattered. As a result, the number of the charged-particles to bescattered, which is detected by the detector 802, is relatively smalland the output signal of the detector 802 is relatively decreased.

In the detector 803, the charged-particle beam transmitting the space,in which the gas molecules are present, is acquired. Thus, if thedensity of gas 804 present between the membrane 10 and the detector 803is great, the number of the charged-particles reaching the detector 803is small and the output signal from the detector 803 is decreased. Onthe other hand, if the density of gas present between the membrane 10and the detector 803 is small, the number of the charged-particlesreaching the detector 803 is great and the output signal from thedetector 803 is increased. It is possible to analyze the gas state underthe membrane 10 by analyzing or comparing the sizes of the signals bydetecting the signals.

Since the signal detected by the detector 802 or the detector 803 is tobe a size corresponding to the amount of charged-particles detected byeach detector, the signal is output as a numeral value or a graph bybeing analyzed by the measurement instrument 806. For example, since thechange in the signal amount can be acquired by continuously applying thecharged-particle beam for a certain time, it is possible to acquire thechange in the signal amount and to display a graph of which a horizontalaxis is time and a vertical axis is the signal amount. The vertical axisis a scattered signal amount and scanning of the charged-particle beamis determined by an atomic weight Z and a pressure P of gas. Thus, ifthe pressure P is constant, the vertical axis may be the atomic weightZ. Otherwise, if the gas type is known, the vertical axis may be thepressure P and when detecting suddenly generated gas and the like, thegraph and the numeral value are not displayed, instead thereof, or inaddition thereto, presence or absence of gas may be known such as lightand buzzer sound. The numeral value and the graph are displayed by amonitor of a computer (not illustrated) connected to the measurementinstrument 806.

Moreover, when acquiring the numeral value and the graph of thedetection signal described above, it becomes erroneous information ifirradiation amount of the charged-particle beam is varied. Thus, acurrent amount from the charged-particle source 8 may be monitored.Monitoring of the current amount is performed by detecting the reflectedcharged-particles, which are reflected on the detector 802 by applyingthe charged-particle beam once to a location such as a base of themembrane (not illustrated) and the charged-particle optical column 800which is not in the membrane 10, or acquiring an absorbing current.Monitoring of the primary charged-particle beam is always orperiodically performed. The operation may be executed by the user or maybe automatically monitored.

In addition, as illustrated in FIGS. 1 and 15, if the configuration ofthe charged-particle optical column 800 includes the optical lenscapable of changing the track, the focus, and the like of thecharged-particle beam and a control section for displaying the image,gas analysis may be performed from the brightness of the image byacquiring the image. As an example, experimental results which areimaged from the signal detected by the detector 3 are illustrated inFIG. 18. FIG. 18 is an example of a case where the pressure of gas belowthe membrane 10, in a state where the sample 6 is not present below themembrane 10 in the apparatus configuration of FIG. 15, is changed to 0.1atm, 0.5 atm, and 1.0 atm. In this case, the detector 3 is positioned onthe charged-particle source side (vacuum space) from the membrane. Ifthe pressure of gas under the membrane 10 is 0.1 atm, since the numberof the charged-particles returning to the detector 3 is small, thesample is looked at dark as the image brightness. On the other hand, ifthe pressure of gas under the membrane 10 is 1.0 atm, since the numberof the charged-particles returning to the detector 3 is great, thesample is looked at bright as the image brightness. Thus, it isindicated that the gas pressure is known from the image brightnessdetected by the detector 3.

Above, the gas pressure is described, but it is similar to the gas type.For example, when comparing helium gas and argon gas, since a size ofatoms of helium gas is very smaller than that of argon gas, thecharged-particle beam is unlikely to be scattered. On the contrary,since the size of atoms of argon gas is very greater than that of heliumgas, the charged-particle beam is likely to be scattered. It is possibleto analyze the gas type by detecting the scattering amount by thedetector 802, the detector 803, and the like.

FIG. 19 illustrates another configuration for detecting gas using theexample. If the method in the example is used, since gas of a very smallregion can be analyzed, as illustrated in FIG. 19(a), it is possible toanalyze gas 804 generated from a specific portion 811 occurred from avery fine region on a base 812. For example, if effective catalysts arewanted to be discovered in catalyst development, various types of thecatalysts are disposed on the base 812, the catalysts are disposed belowthe membrane 10, and thereby it is possible to observe various catalystreaction effects described above. In this case, as described in Examples1 to 5, the base 812 is mounted on the sample stage 5 and it is possibleto dispose the sample stage 5 under the membrane 10 by moving the samplestage 5. In addition, the base 812 is scanned with the charged-particlebeam by moving the stage and the change in the signal amount is analyzedfrom the detector corresponding to a scan position. Thus, it is alsopossible to detect the specific region in which gas is generated.Moreover, a temperature heater capable of changing a temperature and thelike may be provided in the sample stage 5 or the base 812. In addition,as illustrated in FIG. 19(b), a configuration, in which gas 804 that iswanted to be analyzed is put on the inside of a gas sealing container810 including a membrane 809 and the gas sealing container 810 ismounted on the charged-particle optical column 800 including an opening813, may be provided. In this case, the membrane 809 is mounted on thegas sealing container and the membrane is disposed on the side on whichthe charged-particle beam is applied. Gas is analyzed by approaching orcontacting the opening 813 with the gas sealing container 810 includingthe membrane 809 so that the charged-particle beam is not exposed to gasother than gas 814 that is wanted to be analyzed. Vacuum may bemaintained on the inside of the charged-particle optical column 800 by avacuum pump (not illustrated) by making the opening 813 sufficientlysmall. In addition, as illustrated in FIG. 19(c), a membrane 10 isincluded in the charged-particle optical column 800 and the analysis maybe performed by causing the gas sealing container 810 including themembrane 809 described above to approach the membrane 10. In this case,since vacuum is always maintained on the inside of the charged-particleoptical column 800, an exhaust speed of the vacuum pump (notillustrated) for the charged-particle optical column 800 is decreased.Moreover, as described above, since gas analysis of a very small regioncan be performed, it is possible to greatly decrease the size of the gassealing container 810. Thus, according to the method of the example, gas814 that is wanted to be analyzed is also very small.

According to the example, the vacuum space is only the charged-particleoptical column 800 and it is possible to analyze the sample in thenon-vacuum space. Thus, an apparatus for gasification of the analysischamber and a mechanism for introducing the sample into the analysischamber can be unnecessary or simplified, and reduction of the size ofthe apparatus can be achieved. Particularly, since vacuum is maintainedon the inside of the charged-particle optical column that is the vacuumspace as long as the membrane is not damaged, it is also possible to beportable by reduction of the size. In addition, since the sample ispositioned within the non-vacuum space, the vacuum chamber is notpolluted by introduction of the sample. Furthermore, even if themembrane is polluted or damaged, since the membrane is inexpensive, itis possible to simply restore the vacuum chamber to a state of not beingpolluted by exchanging the membrane.

In addition, as illustrated in FIG. 20, the gas sealing container 810that includes the membrane 809 and contains gas 804 that is wanted to beanalyzed may be put into a vacuum space 814 of a generalcharged-particle beam apparatus such as an electronic microscope. Alsoin this case, gas analysis can be performed by signal processing similarto the method described above. In this case, it is possible to use ageneral charged-particle beam apparatus. Thus, gas 804 that is wanted tobe analyzed is only put into the gas sealing container 810 and it ispossible to perform gas analysis very simply without introducing a newapparatus.

The analyzing method of the example can be widely used, particularly, infields of analyzing gas such as a food field, a medical field, materialanalysis, and a chemical industry field. Furthermore, in the example, ifthe apparatus is a very small apparatus, the apparatus can also be usedas a gas sensor that detects presence or absence of gas and the like bymounting on a building and a vehicle.

Moreover, the invention is not limited to the examples described aboveand includes various modification examples. For example, the examplesdescribed above are described in detail in order to easily describe theinvention, but the invention is not limited to the apparatus thatnecessarily includes all configurations described above. In addition, apart of the configurations of a certain example is able to be replacedby the configurations of another example. In addition, theconfigurations of another example can also be added to theconfigurations of a certain example. In addition, for a part of theconfigurations of the examples, it is possible to add, delete, andreplace the other configurations. In addition, a part or all eachconfiguration, the function, the processing section, the processingunit, and the like may be realized as hardware, for example, bydesigning as an integrated circuit. In addition, each configuration, thefunction, and the like described above may be realized as software byinterpreting and executing programs in which a processor realizes eachfunction.

Information of programs, tables, files, and the like realizing eachfunction can be positioned in a recording apparatus such as a memory, ahard disk, and a solid state drive (SSD), or a recording medium such asan IC card, a SD card, and an optical disk.

In addition, the control line and the information line, which arebelieved to be necessary for description, are illustrated and it doesnot necessarily indicate all the control lines and the information lineson products. In practice, almost all of configurations may be consideredto be connected to each other.

REFERENCE SIGNS LIST

-   -   1: optical lens, 2: charged-particle optical column, 3:        detector, 4: vacuum pump, 5: sample stage, 6: sample, 7:        housing, 8: charged-particle source, 9: base, 10: first        membrane, 11: first space, 12: second space, 14: leakage valve,        16: vacuum pipe, 17: stage support base, 18: pillar, 19: lid        member support member, 20: bottom plate, 33: monitor, 34: user        interface such as keyboard and mouse, 35: computer, 36: upper        control section, 37: lower control section, 43, 44, 45:        communication line, 52: sample stage, 53: optical axis, 56:        contact preventing member, 59: irradiation energy control        section, 60: control section, 100: gas supply pipe, 101: gas        control valve, 102: connection section, 103: gas cylinder or        vacuum pump, 104: pressure adjusting valve, 107: support plate,        108, 109: operation knob, 121: second housing, 122, 130: lid        member, 123, 124, 125, 126, 128, 129: vacuum sealing member,        131: body section, 132: mating section, 154: signal amplifier,        155: membrane maintaining member, 200: optical axis, 201:        primary charged-particle beam, 202: primary charged-particle        beam, 203: secondary charged-particle, 210: change in signal        brightness during irradiation energy E1, 211: change in signal        brightness during irradiation energy E2, 212: change in image        resolution during irradiation energy E1, 213: change in image        resolution during irradiation energy E2, 400: data transmitting        and receiving section, 401: data memory section, 402: external        interface, 403: calculation section, 404: stage control section,        501: detection surface, 502: detection surface, 600: detector,        601: hole, 602: primary charged-particle beam, 603: secondary        charged-particle, 604: secondary charged-particle, 605: primary        charged-particle beam, 700: operation screen, 701: condition        setting section, 702: image display section, 703: line profile        display section, 704: image adjusting section, 705: threshold        setting section, 706: irradiation energy E setting section, 707:        irradiation starting button, 708: irradiation stop button, 709:        image storing button, 710: image reading button, 711: brightness        threshold Bz setting section, 712: resolution threshold Dz        setting section, 713: automatic approaching start button, 714:        automatic approaching stop button, 715: focus adjusting section,        716: brightness adjusting section, 717: contrast adjusting        section, 800: charged-particle optical column, 802: detector,        803: detector, 804: gas, 805: gas inlet, 806: measurement        instrument, 807: wiring, 808: optical lens, 809: membrane, 810:        gas sealing container, 811: specific portion, 812: base, 813:        opening, 814: vacuum space

1. A charged-particle beam apparatus comprising: a charged-particleoptical column that irradiates a sample with a primary charged-particlebeam; a housing that forms a part of the charged-particle beam apparatusand that has an inside thereof which is evacuated by a vacuum pump; amembrane which is able to maintain differential pressure between a spacewhich is evacuated and a space in which the sample is disposed, andthrough which the primary charged-particle beam transmits or passes; adetector that detects secondary charged-particles that are obtained byirradiating the sample with the primary charged-particle beam; adistance adjusting mechanism that varies a distance between the sampleand the membrane; and a control section that monitors the distancebetween the sample and the membrane based on a detection signal that isoutput from the detector or an image that is generated from thedetection signal.
 2. The charged-particle beam apparatus according toclaim 1, wherein the control section detects that the distance betweenthe sample and the membrane becomes a specific distance or becomescloser than the specific distance by brightness information orresolution information of the detection signal or brightness orresolution of an image generated from the detection signal when theprimary charged-particle beam is applied by first irradiation energy. 3.The charged-particle beam apparatus according to claim 2, furthercomprising: an irradiation energy control section that variesirradiation energy of the primary charged-particle beam to the sample inat least two or more conditions, wherein the control section acquiresthe image of the sample from the detection signal that is obtained fromthe sample by applying the primary charged-particle beam by secondirradiation energy that is higher than the first irradiation energyafter the distance between the sample and the membrane is detected to bethe specific distance or closer than the specific distance.
 4. Thecharged-particle beam apparatus according to claim 1, wherein thecontrol section monitors the distance between the sample and themembrane based on brightness of a portion that is in a predetermineddistance from an edge of the membrane in the image or a distance of aportion, which is darker than predetermined brightness, from the edge ofthe membrane in the image.
 5. The charged-particle beam apparatusaccording to claim 1, further comprising: a threshold setting sectionthat sets a threshold of a parameter obtained from the detection signalthat is output from the detector or the image that is generated from thedetection signal, wherein the control section monitors whether or not avalue of the parameter reaches the threshold that is set by thethreshold setting section, and wherein the distance between the sampleand the membrane is close by the distance adjusting mechanism until thedistance reaches the threshold.
 6. The charged-particle beam apparatusaccording to claim 5, wherein the parameter is the brightnessinformation or the resolution information of the detection signalgenerated from the sample, or the brightness or the resolution of theimage that is generated from the detection signal.
 7. Thecharged-particle beam apparatus according to claim 5, wherein theparameter is the brightness of the portion that is in the predetermineddistance from the edge of the membrane in the image or the distance ofthe portion, which is darker than the predetermined brightness, from theedge of the membrane in the image.
 8. A sample image acquiring methodusing a charged-particle beam apparatus including a charged-particleoptical column that irradiates a sample with a primary charged-particlebeam; a housing that forms a part of the charged-particle beam apparatusand that has an inside thereof which is evacuated by a vacuum pump; amembrane which is able to maintain differential pressure between a spacewhich is evacuated and a space in which the sample is disposed, andthrough which the primary charged-particle beam transmits or passes; anda detector that detects secondary charged-particles that are obtained byirradiating the sample with the primary charged-particle beam, themethod comprising: a step of monitoring a distance between the sampleand the membrane based on a detection signal that is output from thedetector or an image that is generated from the detection signal.
 9. Thesample image acquiring method according to claim 8, Wherein detecting orrecognizing that the distance between the sample and the membranebecomes a specific distance or becomes closer than the specific distanceby detecting or recognizing brightness information or resolutioninformation of the detection signal or brightness or resolution of animage generated from the detection signal when the primarycharged-particle beam is applied by first irradiation energy, isperformed.
 10. The sample image acquiring method according to claim 9,further comprising: a step of acquiring the image of the sample from thedetection signal when the primary charged-particle beam is applied bysecond irradiation energy that is higher than the first irradiationenergy after the distance between the sample and the membrane isdetected or recognized to be the specific distance or closer than thespecific distance.
 11. The sample image acquiring method according toclaim 8, further comprising: a step of monitoring the distance betweenthe sample and the membrane based on brightness of a portion that is ina predetermined distance from an edge of the membrane in the image or adistance of a portion, which is darker than predetermined brightness,from the edge of the membrane in the image.
 12. The sample imageacquiring method according to claim 8, further comprising: a step ofdetermining a threshold of a parameter obtained from the detectionsignal that is output from the detector or the image that is generatedfrom the detection signal, a step of monitoring whether or not theparameter reaches the threshold, and a step of causing the distancebetween the sample and the membrane to be close to each other until thedistance reaches the threshold.
 13. The sample image acquiring methodaccording to claim 12, wherein the parameter is the brightnessinformation or the resolution information of the detection signalgenerated from the sample, or the brightness or the resolution of theimage that is generated from the detection signal.
 14. The sample imageacquiring method according to claim 12, wherein the parameter is thebrightness of the portion that is in the predetermined distance from theedge of the membrane in the image or the distance of the portion, whichis darker than the predetermined brightness, from the edge of themembrane in the image.